Sputtering target, transparent conductive film and transparent electrode

ABSTRACT

A sputtering target which is composed of a sintered body of an oxide which contains at least indium, tin, and zinc and includes a spinel structure compound of Zn 2 SnO 4  and a bixbyite structure compound of In 2 O 3 . A sputtering target includes indium, tin, zinc, and oxygen with only a peak ascribed to a bixbyite structure compound being substantially observed by X-ray diffraction (XRD).

TECHNICAL FIELD

The present invention relates to a sputtering target prepared bysintering (hereinafter may referred to as sputtering target or as atarget) and a method for preparing a sputtering target. The inventionalso relates to a transparent conductive film obtained by using asputtering target, and a transparent electrode.

BACKGROUND ART

In recent years, development of displays has been remarkable. A liquidcrystal display (LCD), an electroluminescence display (EL), a fieldemission display (FED), or the like is used as a display device forbusiness machines such as a personal computer and a word processor, anda display device for control systems in factories. These displays have asandwich structure in which a display device is held between transparentconductive oxides.

A main stream material for such a transparent conductive oxide is indiumtin oxide (hereinafter may abbreviated as “ITO”) prepared by asputtering method, an ion plating method, or a vapor deposition methodas described in Non-patent Document 1.

ITO is composed of a specific amount of indium oxide and tin oxide,possesses excellent transparency and conductivity, can be etched using astrong acid, and exhibits high adhesion to a substrate.

Although ITO has excellent properties as a material for transparentconductive oxide, ITO is not only a scarce resource, but also contains alarge amount (about 90 atomic percent) of indium which is a biologicallyharmful element. Moreover, the indium itself produces nodules(projections) during sputtering. The nodules produced on the targetsurface have been one of the causes of abnormal electrical discharge. Inparticular, when an amorphous ITO film is produced for improving etchingproperties, the indium compound on the surface of the target is reduceddue to introduction of a small amount of water and hydrogen gas in thesputtering chamber, giving rise to further production of nodules. If anabnormal electrical discharge occurs, scattered materials becomeattached to the transparent conductive oxide as impurities during orimmediately after the film formation.

The indium content in ITO must be reduced due to these problems ofinstability of supply (scarcity) and hazardous properties. However, themaximum solid solubility limit of tin oxide to indium oxide isconsidered to be about 10%. If the content of indium in ITO is reducedto 90 atomic percent or less, tin oxide remains in the target in theform of a cluster. Since the resistance of tin oxide is 100 or moretimes stronger than the resistance of ITO, the remaining tin oxidecauses charges to accumulate during sputtering, which causes arcing,destroys the target surface, causes small fragments to scatter, andgenerates nodules and particles (Non-patent Document 2). Therefore, itis difficult to reduce the content of indium to 90 atomic percent orless.

As a method for preventing generation of nodules and suppressingabnormal electrical discharge, a hexagonal layered compound ofIn₂O₃(ZnO)_(m), wherein m is an integer of 2 to 20, with a crystal graindiameter of 5 μm or less has been investigated (Patent Documents 1 and2). However, if the indium content is reduced to 90 to 70 atomic percentor less in this method, there are problems such as decrease of thesintered density and conductivity of the target, which causes abnormalelectrical discharge and retards the film forming speed; low targetstrength, leading to easy cracking; and poor heat resistance in thepresence of air of the transparent conductive film formed by sputtering.Moreover, a high temperature is required in order to produce thehexagonal layered compound in a stable manner. This brings about anotherproblem of a high industrial manufacturing cost. Furthermore, thehexagonal layered compound has no resistance to an etching solutioncontaining phosphoric acid used for etching of a metal or an alloy. Thusetching of the metal or alloy membrane formed on the film of thehexagonal layered compound is difficult.

As a transparent conductive film with a significantly reduced indiumcontent, a transparent conductive film containing zinc oxide and tinoxide as major components has been studied (Patent Document 3). However,this method has problems such as difficulty in sputtering due to undulyhigh target resistance and a tendency of easy generation of abnormalelectrical discharge. No study of a sputtering target to solve theseproblems has been undertaken.

Patent Document 4 discloses a zinc oxide sintered body doped withdifferent kinds of elements containing a spinel structure (ZnX₂O₄,wherein X is an element with a positive trivalent or higher valency).However, no studies have been done on the effect of a sintered bodyhaving both a spinel structure compound of Zn₂SnO₄ and a bixbyitestructure compound of In₂O₃.

Although the ITO target which is a sintered body essentially consistingof a bixbyite structure compound of In₂O₃ has been studied (PatentDocument 5), Sn₃In₄O₁₂ and the like are easily produced in the ITOtarget. Even if a sintered body essentially consisting of a bixbyitestructure compound could be produced, only a narrow range ofmanufacturing conditions is allowed. Stable production of such an ITOtarget has been difficult. If the content of indium is reduced,production of a sintered body essentially consisting of a bixbyitestructure compound is difficult.

It is known that in the IZO target which composed of indium and zinc, ahexagonal layered compound of In₂O₃(ZnO)_(m), wherein m is an integer of2 to 20, is formed when the Zn content is 15 to 20 atomic percent(Non-patent Document 3). These crystal types have an effect ofdecreasing the target resistance and increasing the relative density ascompared with ZnO. However, if the amount of indium is reduced (or theamount of zinc is increased), problems such as a decrease in the targetstrength and retardation of the film-forming speed may occur byincreased target resistance and described relative density.

On the other hand, due to the progress of liquid crystal displayfunctions in recent years, it has become necessary to use an electrodesubstrate with a metal or an alloy disposed on a transparent conductivefilm, such as an electrode substrate for a semi-transmissive,semi-reflective liquid crystal.

Patent Document 6 discloses a liquid crystal display device which has atransmissive region and a reflective region on a transparent conductivefilm. Patent Document 7 discloses that a film forming-etching processcan be simplified by using a transparent conductive film possessingselective etching properties, that is, a transparent conductive filmwhich is etched by an acid not corrosive to a metal, but is resistant toand etched only with difficulty by an etching solution used for etchingmetals. However, the method of Patent Document 7 may change thecrystallization temperature and the work function of a transparentconductive film due to the addition of lanthanoids. Moreover, it isnecessary to add lanthanoid oxide, which is a scarce resource, to thetransparent conductive film in order to adjust the etching rate.Furthermore, there is almost no reduction in the indium content of thetransparent conductive film.

[Patent Document 1] WO 01/038599 [Patent Document 2] JP-A-06-234565[Patent Document 3] JP-A-08-171824 [Patent Document 4] JP-A-03-50148[Patent Document 5] JP-A-2002-030429 [Patent Document 6]JP-A-2001-272674 [Patent Document 7] JP-A-2004-240091

[Non-patent Document 1] “Technology of Transparent Conductive Film”edited by The 166th Committee of Transparent Oxide and PhotoelectronMaterial, Japan Society for Promotion of Science, Ohmsha, Ltd. (1999)

[Non-patent Document 2] Ceramics, 37 (2002), No. 9, pp 675-678[Non-patent Document 3] Journal of the American Ceramic Society, 81(5),1310-16 (1998))

An object of the invention is to provide a target with low resistance,high theoretical relative density, and high strength, a target with areduced indium content, a target which allows stable sputtering whilesuppressing abnormal electrical discharge generated when forming atransparent conductive film by the sputtering method, a method forproducing the targets, and a transparent conductive film produced usingthe sputtering targets.

Another object of the invention is to provide a transparent conductivefilm which can be selectively etched relative to a metal or an alloy,that is, a transparent conductive film which is etched by an acid notcorrosive to a metal or an alloy, but is resistant to or is hardlyetched by an etching solution used for etching the metal or alloy.

Still another object of the invention is to provide a transparentconductive film exhibiting a small increase in resistance during a heattreatment in the atmosphere and a small resistance distribution in alarge area.

A further object of the invention is to provide a transparent electrodeand an electrode substrate made from these transparent conductive films.

A still further object of the invention is to provide a simplifiedmethod for producing an electrode substrate from these transparentconductive films.

DISCLOSURE OF THE INVENTION

An oxide sintered target containing indium, tin, and zinc as majorcomponents may contain a hexagonal layered compound of In₂O₃(ZnO)_(m),wherein m is an integer of 2 to 20, a rutile structure compound of SnO₂,a wurtzite form compound of ZnO, a spinel structure compound of Zn₂SnO₄,a bixbyite structure compound of In₂O₃, a spinel structure compound ofZnIn₂O₄, and other crystal structures such as ZnSnO₃, Sn₃In₄O₁₂, and thelike, depending on the form of raw materials, thermal history duringsintering, the method of heat treatment, the content of components, andthe like. Various combinations of these crystal structures are possible.

The inventors of the invention have found that among many combinationsof the compounds, a combination of a spinel structure compound ofZn₂SnO₄ and a bixbyite structure compound of In₂O₃ has a low resistanceand a high theoretical relative density, and can form a target with ahigh strength. Although the reason for this effect cannot completely beelucidated, it is assumed that under specific sintering conditions inspecific compositions, In is easily dissolved as a solid solute in aspinel structure compound of Zn₂SnO₄, and Sn and the like are easilydissolved as a solid solute in a bixbyite structure compound of In₂O₃.That is, it is assumed that when positive divalent Zn exists, positivetetravalent Sn is easily dissolved in In₂O₃ containing positivetrivalent In as a solid solute, whereas when positive divalent Zn andpositive tetravalent Sn are present in proximate, positive trivalent Inis easily dissolved in Zn₂SnO₄ as a solid solute.

Moreover, the inventors of the invention have found that if the crystalstructure of a target is substantially a bixbyite structure, the targetcan exhibit the same etching workability as IZO and the same filmperformance as the ITO, even if the indium content is reduced to 60 to75 atomic percent.

The inventors of the invention have further found that the transparentconductive film formed by the sputtering method using these targetsexcels in conductivity, etching properties, heat resistance, and thelike, and is suitable for various applications such as a displayrepresented by a liquid crystal display, a touch panel, a solar cell,and the like even if the content of indium is reduced.

The inventors have further found that since stable sputtering can becarried out, these targets can be used for forming a transparent oxidesemiconductor typified by a thin film transistor (TFT) by adjusting thefilm-forming conditions and the like.

The inventors have further found that a transparent conductive filmcontaining indium, tin, and zinc at a specific atomic ratio can beselectively etched relative to a metal or an alloy.

According to the invention, the following sputtering target, method forproducing the same, transparent conductive film, and transparentelectrode are provided.

1. A sputtering target which is composed of a sintered body of an oxidecomprising at least indium, tin, and zinc and comprising a spinelstructure compound of Zn₂SnO₄ and a bixbyite structure compound ofIn₂O₃.2. The sputtering target according to 1, wherein the atomic ratio ofIn/(In+Sn+Zn) is in a range of 0.25 to 0.6, the atomic ratio ofSn/(In+Sn+Zn) is in a range of 0.15 to 0.3, and the atomic ratio ofZn/(In+Sn+Zn) is in a range of 0.15 to 0.5.3. The sputtering target according to 1 or 2, wherein in an X-raydiffraction (XRD), the ratio of the maximum peak intensity of the spinelstructure compound of Zn₂SnO₄ (I(Zn₂SnO₄)) to the maximum peak intensityof the bixbyite structure compound of In₂O₃ (I(In₂O₃)),I(Zn₂SnO₄)/I(In₂O₃), is in a range of 0.05 to 20.4. The sputtering target according to any one of 1 to 3, wherein, in anX-ray diffraction (XRD), the maximum peak intensity of the rutilestructure compound of SnO₂ (I(SnO₂)), the maximum peak intensity of thespinel structure compound of Zn₂SnO₄ (I(Zn₂SnO₄)), and the maximum peakintensity of the bixbyite structure compound of In₂O₃ (I(In₂O₃)) havethe following relationship:

I(SnO₂)<I(Zn₂SnO₄) I(SnO₂)<I(In₂O₃) I(SnO₂)<Max. (I(Zn₂SnO₄),I(In₂O₃))÷10

wherein Max. (X,Y) indicates the larger of either X or Y.5. The sputtering target according to any one of 1 to 4, wherein in anX-ray diffraction (XRD), the maximum peak intensity of the wurtzitestructure compound of ZnO (I(ZnO)), the maximum peak intensity of thespinel structure compound of Zn₂SnO₄ (I(Zn₂SnO₄)), and the maximum peakintensity of the bixbyite structure compound of In₂O₃ (I(In₂O₃)) havethe following relationship:

I(ZnO)<I(Zn₂SnO₄) I(ZnO)<I(In₂O₃) I(ZnO)<Max. (I(Zn₂SnO₄), I(In₂O₃))÷10

wherein Max. (X,Y) indicates the larger of either X or Y.6. The sputtering target according to any one of 1 to 5, wherein, in anX-ray diffraction (XRD), the maximum peak intensity of the hexagonallayered compound of In₂O₃(ZnO)_(m), wherein m is an integer of 2 to 20,(I/In₂O₃(ZnO)_(m)), the maximum peak intensity of the spinel structurecompound of Zn₂SnO₄ (I(Zn₂SnO₄)), and the maximum peak intensity of thebixbyite structure compound of In₂O₃ (I(In₂O₃)) have the followingrelationship:

I(In₂O₃ (ZnO)<I(Zn₂SnO₄) I(In₂O₃ (ZnO)_(m))<I(In₂O₃) I(In₂O₃ZnO)_(m))<Max. (I(Zn₂SnO₄), I(In₂O₃)÷10

wherein Max. (X,Y) indicates the larger of either X or Y.7. The sputtering target according to any one of 1 to 6, wherein, in theimage of an electron probe micro analyzer (EPMA), indium rich partsS(In) and lead rich parts S Zn) form a sea-island structure with a ratioof the areas S Zn)/S(In) in a range of 0.05 to 100.8. The sputtering target according to any one of 1 to 7, wherein thebixbyite structure compound of In₂O₃ has a crystal grain diameter of 10μm or less.9. The sputtering target according to any one of 1 to 8, of which thebulk resistance is in a range of 0.3 to 100 mΩ·cm.10. The sputtering target according to any one of 1 to 9, having atheoretical relative density of 90% or more.11. A method for producing the sputtering target according to any one of1 to 10, comprising the steps of:

preparing a mixture of a powder of an indium compound, a powder of azinc compound, and a powder of a tin compound having a particle diametersmaller than the particle diameters of the powders of the indiumcompound and the zinc compound at an atomic ratio of In/(In+Sn+Zn) in arange of 0.25 to 0.6, an atomic ratio of Sn/(In+Sn+Zn) in a range of0.15 to 0.3, and an atomic ratio of Zn/(In+Sn+Zn) in a range of 0.15 to0.5;

press-molding the mixture to obtain a molded product; and

sintering the molded product.

12. A transparent conductive film obtained by sputtering the sputteringtarget according to any one of 1 to 10.13. A transparent electrode obtained by etching the transparentconductive film according to 12.14. A sputtering target comprising indium, tin, zinc, and oxygen withonly a peak ascribed to a bixbyite structure compound beingsubstantially observed by an X-ray diffraction (XRD).15. The sputtering target according to 14, wherein the bixbyitestructure compound is shown by In₂O₃.16. The sputtering target according to 14 or 15, wherein the atomicratio of In/(In+Sn+Zn) is in a range larger than 0.6 and smaller than0.75, and the atomic ratio of Sn/(In+Sn+Zn) is in a range of 0.11 to0.23.17. The sputtering target according to any one of 14 to 16, wherein, inan X-ray diffraction (XRD), the maximum peak position of the bixbyitestructure compound shifts toward the plus direction (wide angle side)compared to an In₂O₃ single crystal powder.18. The sputtering target according to any one of 14 to 17, wherein theaverage diameter of Zn aggregates observed by an electron probe microanalyzer (EPMA) is 50 μm or less. 19. The sputtering target according toany one of 14 to 18, wherein the content of each of Cr and Cd is 10 ppm(by mass) or less.20. The sputtering target according to any one of 14 to 19, wherein thecontent of each of Fe, Si, Ti, and Cu is 10 ppm (by mass) or less.21. The sputtering target according to any one of 14 to 20, wherein thebixbyite structure compound has a crystal grain diameter of 20 μm orless.22. The sputtering target according to any one of 14 to 21, of which thebulk resistance is in a range of 0.2 to 100 mΩ·cm.23. The sputtering target according to any one of 14 to 22, having atheoretical relative density of 90% or more.24. A method for producing a sputtering target comprising the steps of:

preparing a mixture of raw material compounds of indium, tin, and zincat an atomic ratio of In/(In+Sn+Zn) in a range larger than 0.6 andsmaller than 0.75, and an atomic ratio of Sn/(In+Sn+Zn) in a range of0.11 to 0.23;

press-molding the mixture to obtain a molded product;

heating the molded product at a rate of 10 to 1,000° C./hour;

firing the molded product at a temperature in a range of 1,100 to 1,700°C. to obtain a sintered body; and

cooling the sintered body at a rate of 10 to 1,000° C./hour.

25. A transparent conductive film obtained by sputtering the sputteringtarget according to any one of 14 to 23.26. A transparent electrode obtained by etching the transparentconductive film according to 25.27. The transparent electrode according to 26, having a taper angle atan electrode edge of 30 to 89°.28. A method for forming a transparent electrode comprising etching thetransparent conductive film according to 25 with a 1 to 10 mass % oxalicacid aqueous solution at a temperature in a range of 25 to 50° C.29. A transparent conductive film comprising an amorphous oxide ofindium (In), zinc (Zn), and tin (Sn), satisfying the following atomicratio 1 when the atomic ratio of Sn to In, Zn, and Sn is 0.20 or less,and the following atomic ratio 2 when the atomic ratio of Sn to In, Zn,and Sn is more than 0.20;

Atomic Ratio 1: 0.50<In/(In+Zn+Sn)<0.75 0.11<Sn/(In+Zn+Sn)≦0.200.11<Zn/(In+Zn+Sn)<0.34 Atomic Ratio 2: 0.30<In/(In+Zn+Sn)<0.600.20<Sn/(In+Zn+Sn)<0.25 0.14<Zn/(In+Zn+Sn)<0.46

30. The transparent conductive film according to 29, having a ratio ofthe etching rate B when etched with an etching solution containingoxalic acid to the etching rate A when etched with an etching solutioncontaining phosphoric acid (B/A) of 10 or more.31. A transparent electrode comprising the transparent conductive filmaccording to 29 or 30 with a taper angle of 30 to 89°.32. An electrode substrate comprising the transparent electrodecomprising the transparent conductive film according to 29 or 30 and alayer of a metal or an alloy.33. The electrode substrate according to 32, wherein the metal or alloycomprises an element selected from the group consisting of Al, Ag, Cr,Mo, Ta, and W.34. The electrode substrate according to 32 or 33, which is to be usedfor a semi-transmissive, semi-reflective liquid crystal.35. The electrode substrate according to any one of 32 to 34, whereinthe layer of the metal or alloy is an auxiliary electrode.36. A method for producing the electrode substrate according to any oneof 32 to 35 comprising the steps of:

preparing a transparent conductive film;

forming a layer of a metal or an alloy at least on a part of thetransparent conductive film;

etching the layer of a metal or alloy with an etching solutioncontaining an oxo acid; and

etching the transparent conductive film with an etching solutioncontaining a carboxylic acid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing showing an X-ray diffraction chart of the targetproduced in Example 1.

FIG. 2 is a drawing showing an X-ray diffraction chart of the targetproduced in Example 3.

FIG. 3 is a drawing showing an X-ray diffraction chart of the targetproduced in Example 4.

FIG. 4 is a schematic drawing showing the sea-island structure in whichan indium (In) rich phase and a zinc (Zn) rich phase are separated inthe target of the invention in elementary analysis of the targetcross-section by an electron probe micro analyzer (EPMA).

FIG. 5 shows an elementary analysis image of the target cross-section ofthe target produced in Example 1 taken by an electron probe microanalyzer (EPMA).

FIG. 6 shows an elementary analysis image of the target cross-section ofthe target produced in Comparative Example 1 taken by an electron probemicro analyzer (EPMA).

FIG. 7 is a drawing showing an X-ray diffraction chart of the targetproduced in Example 6.

FIGS. 8( a) to 8(e) are drawings schematically showing a method ofproducing an electrode substrate in Example 10.

BEST MODE FOR CARRYING OUT THE INVENTION

A first aspect of the invention is described below.

I. Sputtering Target

The sputtering target of the first aspect (hereinafter referred to as“target of the first aspect”) is a sintered body of an oxide whichcontains at least indium, tin, and zinc and includes a spinel structurecompound of Zn₂SnO₄ and a bixbyite structure compound of In₂O₃. Thetarget of the first aspect is preferably a sintered body of an oxidewhich consists essentially of a spinel structure compound of Zn₂SnO₄ anda bixbyite structure compound of In₂O₃.

As mentioned above, the target is provided with low resistance, hightheoretical relative density, and high strength due to inclusion of boththe spinel structure compound shown by Zn₂SnO₄ and the bixbyitestructure compound shown by In₂O₃.

The spinel structure will now be explained.

As described in “Crystal Chemistry” (M. Nakahira, Kodansha, 1973) andthe like, an AB₂X₄ type or an A₂BX₄ type is called a spinel structure,and a compound having such a crystal structure is called a spinelstructure compound in general.

In a common spinel structure, anions (usually oxygen) are filled bycubic closest packing with cations being present in part of tetrahedronor octahedron clearances.

A substituted-type solid solution in which some of the atoms and ions inthe crystal structure are replaced with other atoms and an interstitialsolid solution in which other atoms are added to the sites betweengratings are also included in the spinel structure compounds.

The spinel structure compound of the target of the first aspect is acompound shown by Zn₂SnO₄. That is, in X-ray diffraction, the compoundshows a peak pattern of No. 24-1470 or an analogous (shifted) pattern ofthe Joint Committee on Powder Diffraction Standards (JCPDS) database.

Next, the bixbyite structure compound is described. A bixbyite structurecompound is also referred to as a rare earth oxide C-type or Mn₂O₃(I)-type oxide. As described in “Technology of Transparent ConductiveFilm” edited by The 166th Committee of Transparent Oxide andPhotoelectron Material, Japan Society for Promotion of Science, Ohmsha,Ltd. (1999) and the like, the bixbyite structure compound has astoichiometric ratio of M₂X₃, wherein M is a cation and X is an anion,usually an oxygen ion, and one unit cell is composed of 16 molecules ofM₂X₃ and the total 80 atoms (32 Ms and 48 Xs). Among these, the bixbyitestructure compound of the target of the first aspect is a compound shownby In₂O₃, that is, a compound having a peak pattern of No. 06-0416 or ananalogous (shifted) pattern of the Joint Committee on Powder DiffractionStandards (JCPDS) database in X-ray diffraction.

A substituted-type solid solution in which some of the atoms and ions inthe crystal structure are replaced with other atoms and an interstitialsolid solution in which other atoms are added to the sites betweengratings are also included in the bixbyite structure compounds.

The crystal conditions of the compound in the target can be judged byobserving a sample extracted from the target (sintered body) by X-raydiffraction analysis.

The target of the first aspect preferably has an atomic ratio ofIn/(In+Sn+Zn) in a range of 0.25 to 0.6, an atomic ratio ofSn/(In+Sn+Zn) in a range of 0.15 to 0.3, and an atomic ratio ofZn/(In+Sn+Zn) in a range of 0.15 to 0.5.

The above atomic ratios of the target of the first aspect can bemeasured by inductively coupled plasma (ICP) spectrophotometry.

If the atomic ratio of In/(In+Sn+Zn) is less than 0.25, the target mayhave high bulk resistance and a low density, and the resistance of thetransparent conductive film obtained by sputtering the target mayincrease. If more than 0.6, indium reduction may be insufficient.

If the atomic ratio of Sn/(In+Sn+Zn) is less than 0.15, the target mayhave reduced strength and increased bulk resistance. Moreover, the heatresistance under atmosphere of the transparent conductive film obtainedby sputtering may decrease, durability after connection with wiring maybe impaired due to increased contact resistance, and there is apossibility that the probe inspection cannot be done. If larger than0.3, wet etching may become difficult.

If the atomic ratio of Zn/(In+Sn+Zn) is less than 0.15, wet etching maybe difficult; if larger than 0.5, the transparent conductive filmobtained by sputtering may have decreased heat resistance andconductivity.

If the atomic ratio is outside of the above-mentioned range, there is apossibility that the spinel structure compound of Zn₂SnO₄ and thebixbyite structure of In₂O₃ cannot be included in the target at the sametime even if the sintering conditions are changed.

The atomic ratio of In/(In+Sn+Zn) is preferably in a range of 0.26 to0.59, more preferably 0.26 to 0.52, and particularly preferably 0.31 to0.49.

The atomic ratio of Sn/(In+Sn+Zn) is preferably in a range of 0.17 to0.24, more preferably 0.19 to 0.24, and particularly preferably 0.21 to0.24.

The atomic ratio of Zn/(In+Sn+Zn) is preferably in a range of 0.19 to0.49, more preferably 0.2 to 0.49, and particularly preferably 0.21 to0.45.

In the target of the first aspect, for peaks in an X-ray diffraction(XRD), the ratio of the maximum peak intensity of the spinel structurecompound of Zn₂SnO₄ (I(Zn₂SnO₄)) to the maximum peak intensity of thebixbyite structure compound of In₂O₃ (I(In₂O₃)), I(Zn₂SnO₄)/I(In₂O₃), ispreferably in a range of 0.05 to 20.

If the ratio of the maximum peak intensity I(Zn₂SnO₄)/I(In₂O₃) is lessthan 0.05, the amount of the spinel structure compound of Zn₂SnO₄ issmall. It may be difficult for the density of the target to increaseunless heated to a high temperature, the strength of the target mayeasily decrease, and abnormal electrical discharge may easily occur dueto production of a very small amount of SnO (an insulator) resultingfrom unstable solid dissolution of Sn in In₂O₃. If the ratio of themaximum peak intensity (I(Zn₂SnO₄)/I(In₂O₃)) is larger than 20, theamount of the bixbyite structure compound of In₂O₃ is small. In thiscase, the resistance of the target may be high.

The above-mentioned ratio of the maximum peak intensity(I(Zn₂SnO₄)/I(In₂O₃)) is more preferably in a range of 0.1 to 10, morepreferably 0.15 to 7, particularly preferably 0.2 to 5, and mostpreferably 0.7 to 4.

The ratio of the maximum peak intensity can be determined by calculatingfrom the maximum peak intensity which is present in an arbitrary range(for example, the range of 28=15 to)65° using a chart produced by X-raydiffraction (XDR).

In the case in which it is desired to particularly reduce the resistanceof the target, the ratio of the maximum peak intensity(I(Zn₂SnO₄)/I(In₂O₃)) is preferably larger than 1. In the case in whichit is desired to increase the sintered density, the ratio of the maximumpeak intensity (I(Zn₂SnO₄)/I(In₂O₃)) is preferably smaller than 1.

Furthermore, it is preferable that both the spinel structure compound ofZn₂SnO₄ and the bixbyite structure compound of In₂O₃ have a maximum peakstrength larger than the maximum peak strength of other compounds toexhibit their effects.

In regard to peaks in an X-ray diffraction (XRD) in the target of thefirst aspect, it is preferable that the maximum peak intensity of therutile structure compound of SnO₂ (I(SnO₂)), the maximum peak intensityof the spinel structure compound of Zn₂SnO₄ (I(In₂SnO₄)), and themaximum peak intensity of the bixbyite structure compound of In₂O₃(I(In₂O₃)) satisfy the following relationship:

I(SnO₂)<I(Zn₂SnO₄) I(SnO₂)<I(In₂O₃) I(SnO₂)<Max. (I(Zn₂SnO₄),I(In₂O₃))÷10

wherein Max. (X,Y) indicates the larger of either X or Y.

In regard to peaks in an X-ray diffraction (XRD) of the sputteringtarget of the first aspect, it is preferable that the maximum peakintensity of the wurtzite structure compound of ZnO (I(ZnO)), themaximum peak intensity of the spinel structure compound of Zn₂SnO₄(I(Zn₂SnO₄)) and the maximum peak intensity of the bixbyite structurecompound of In₂O₃ (I(In₂O₃) satisfy the following relationship:

I(ZnO)<I(Zn₂SnO₄) I(ZnO)<I(In₂O₃) I(ZnO)<MAX. (I(Zn₂SnO₄), I(In₂O₃))÷10

wherein Max. (X,Y) indicates the larger of either X or Y.

The above relationship formula indicates that the target of the firstaspect contains only a small amount of the rutile structure compound ofSnO₂ and/or the wurtzite form compound of ZnO, or does not substantiallycontain these compounds.

The rutile structure compound is an AX₂-type compound having chains ofregular octahedrons which share an edge running parallel to the L axisof tetragonal system and cations arranged in the form of a body-centeredtetragonal lattice. Among these compounds, the rutile structure compoundof the target of the first aspect is a compound shown by SnO₂.

A wurtzite form compound is a four-coordinated, hexagonal packingAX-type compound. Among these compounds, the wurtzite form compound ofthe target of the first aspect is a compound shown by ZnO.

Further, it is preferable that the target of the first aspect does notsubstantially contain a complex oxide of Sn₃In₄O₁₂.

The complex oxide shown by Sn₃Zn₄O₁₂ is described in “Materia” Vol. 34,No. 3, pp 344-351 (1995), for example.

If the target of the first aspect contains a large amount of the rutilestructure compound of SnO₂ or the wurtzite form compound of ZnO,problems such as an increase in the bulk resistance of the target, adecrease in the relative density of the target, and the like may occur.

If the target contains the complex oxide of Sn₃In₄O₁₂, a slow sputteringrate of Sn₃In₄O₁₂ may produce nodules.

In regard to peaks in an X-ray diffraction (XRD) of the target of thefirst aspect, the maximum peak intensity of hexagonal layered compoundof In₂O₃(ZnO)_(m), wherein m is an integer of 2 to 20,(I/In₂O₃(ZnO)_(m)), the maximum peak intensity of the spinel structurecompound of Zn₂SnO₄ (I(Zn₂SnO₄)), and the maximum peak intensity of thebixbyite structure compound of In₂O₃ (I(In₂O₃)) preferably satisfyfollowing relationship:

I(In₂O₃(ZnO)_(m))<I(Zn₂SnO₄) I(In₂O₃(ZnO)_(m))<I(In₂O₃)I(In₂O₃(ZnO)_(m))<Max. (I(Zn₂SnO₄), I(In₂O₃))÷10

wherein Max. (X,Y) indicates the larger of either X or Y.

The above formulas indicate that the target of the first aspect does notsubstantially contain or contains only a small amount of the hexagonallayered compound of In₂O₃(ZnO)_(m), wherein m is an integer of 2 to 20.

The hexagonal layered compound is a compound described in L. Dupont etal., Journal of Solid State Chemistry 158, 119-133 (2001), ToshihiroMoriga et al., J. Am. Ceram. Soc., 81(5), 1310-16 (1998), and the like.The hexagonal layered compound in the first aspect refers to a compoundshown by In₂O₃(ZnO)_(m), wherein m is an integer of 2 to 20, orZn_(k)In₂O_(k+3), wherein k is an integer.

If the target of the first aspect contains a large amount of thehexagonal layered compound of In₂O₃(ZnO)_(m), wherein m is an integer of2 to 20, the target may have a high resistance, may produce abnormalelectrical discharge, and may be easily cracked due to insufficientstrength.

In elementary analysis of the cross-section of the target of the firstaspect by an electron probe micro analyzer (EPMA), an indium (In) richpart (hereinafter referred to as an indium (In) rich phase) and a zinc(Zn) rich part (hereinafter referred to as a zinc (Zn) rich phase) forma separated sea-island structure (a schematic drawing is shown in FIG.4) and the ratio of the indium area S(In) to the zinc area S(Zn),S(Zn)/S(In), is preferably in a range of 0.05 to 100. The areas S(In)and S(Zn) are calculated from images of In and Zn. The ratio of theareas, S(Zn)/S(In), is more preferably 0.05 to 20, still more preferably0.1 to 10, and particularly preferably 0.2 to 5.

A rich phase means an area with a higher element density (usually 1.5 to2 times or more) than the element density of the surrounding area byEPMA analysis.

If the indium (In) rich phase and the zinc (Zn) rich phase do not have asea-island structure or the ratio of the areas S(Zn)/S(In) is not in therange of 0.05 to 100, the density of the target may be reduced, the bulkresistance may be increased, or the strength may be decreased. Inparticular, when these phases do not have a sea-island structure, thebulk resistance tends to become high. The reason is probably as follows.That is, if the sea-island structure is not formed, a large amount ofpositive divalent Zn is dissolved as a solid in a positive terivalent Incompound and carriers are trapped. The carrier trap reduces the densityof carriers and increases the bulk density.

In the target of the first aspect, crystals of the bixbyite structurecompound of In₂O₃ have a particle diameter preferably of 10 μm or less,more preferably 6 μm or less, and particularly preferably 4 μm or less.

If the crystal grain diameter of the bixbyite structure compound ofIn₂O₃ is more than 10 μm, abnormal electrical discharge and nodules maybe caused.

The crystal grain diameter of each compound can be measured using anelectron probe micro analyzer (EPMA).

It is preferable that the target of the first aspect have a bulkresistance of 100 mΩ·cm or less and a theoretical relative density of90% or more.

If the bulk resistance of the target is high or theoretical relativedensity is less than 90%, the target may crack during discharge.

The bulk resistance of the target of the first aspect is more preferablyin the range of 0.3 to 50 mΩ·cm, still more preferably 0.3 to 10 mΩ·cm.,particularly preferably 0.4 to 5 mΩ·cm, and most preferably 0.4 to 3mΩ·cm.

The bulk resistance of the target is measured by the four probe method.

Theoretical relative density of the target of the first aspect is morepreferably 95% or more, and particularly preferably 98% or more. Iftheoretical relative density is less than 90%, the target may havereduced strength or exhibit a retarded film-forming speed, or a filmproduced by sputtering the target may have a high resistance.

Theoretical relative density is determined as follows.

The density of the target is calculated from the content ratio of ZnO,SnO₂, and In₂O₃ assuming that their specific gravities are respectively5.66 g/cm³, 6.95 g/cm³, and 7.12 g/cm³. Then, the ratio of thecalculated density to the density measured by Archimedes principle iscalculated. The resulting value is used as theoretical relative density.

The deflecting strength of the target of the first aspect is preferably10 kg/mm² or more, more preferably 11 kg/mm² or more, and particularlypreferably 12 kg/mm² or more. There is a possibility that the target maybe damaged due to the load applied during transportation andinstallation. For this reason, the target needs to have deflectingstrength of a degree not less than a certain level. If the deflectingstrength is less than 10 kg/mm², the target may not be usable.

The deflecting strength of the target can be measured according to JISR1601.

II. Method for Producing Sputtering Target

The method for producing the sputtering target of the first aspect(hereinafter may referred to as “method of the first aspect”) comprisesa step of obtaining a mixture of a powder of an indium compound, apowder of a zinc compound, and a powder of a tin compound having aparticle diameter smaller than those of the powder of the indiumcompound and the powder of the zinc compound in a proportion to make anatomic ratio of In/(In+Sn+Zn) in a range of 0.25 to 0.6, an atomic ratioof Sn/(In+Sn+Zn) in a range of 0.15 to 0.3, and an atomic ratio ofZn/(In+Sn+Zn) in a range of 0.15 to 0.5, a step of press-molding themixture to obtain a molded product, and a step of sintering the moldedproduct.

Each step of the method of the first aspect is described below.

(1) Mixing Step

The mixing step is an essential step of mixing the raw materials of thesputtering target such as a metal oxide.

As the raw materials, a powder of an indium compound, a powder of a zinccompound, and a powder of a tin compound having a particle diametersmaller than those of the powder of the indium compound and the powderof the zinc compound are used. If the particle diameter of the powder ofthe tin compound is equal to or larger than those of the powder of theindium compound and the powder of the zinc compound, SnO₂ may remain inthe target and may increase the bulk resistance of the target.

In addition, it is preferable that the particle diameter of the powderof the tin compound be smaller than the particle diameters of the powderof the indium compound and the powder of the zinc compound. Morepreferably, the particle diameter of the powder of the tin compound isone half or less of the particle diameters of the powder of the indiumcompound. It is particularly preferable that the particle diameter ofthe powder of the zinc compound be smaller than that of the powder ofthe indium compound.

The particle diameters of the metal compounds used as the raw materialof the target can be measured according to JIS R1619.

The oxides of indium, tin, and zinc which are the raw materials of thetarget must be mixed in a proportion to make the atomic ratio ofIn/(In+Sn+Zn) in a range of 0.25 to 0.6, the atomic ratio ofSn/(In+Sn+Zn) in a range of 0.15 to 0.3, and the atomic ratio ofZn/(In+Sn+Zn) in a range of 0.15 to 0.5. If the ratios are outside theabove ranges, the target of the first aspect having the above-mentionedadvantages cannot be obtained.

As examples of the indium compounds, indium oxide, indium hydroxide, andthe like can be given.

As examples of the tin compounds, tin oxide, tin hydroxide, and the likecan be given.

As examples of the zinc compounds, zinc oxide, zinc hydroxide, and thelike can be given.

Among these compounds, oxides are preferable due to ease of sinteringand almost no leaving byproduct residues.

The purity of the raw materials is usually 2N (99 mass %) or more,preferably 3N (99.9 mass %) or more, and particularly preferably 4N(99.99 mass %) or more. If the purity is less than 2N, heavy metals suchas Cr and Cd may be contained. Such heavy metals may impair durabilityof the transparent conductive film prepared by using the target, and maycause a hazardous end product.

The raw materials such as metal oxides used for producing the target,which satisfy the above-mentioned particle size relationship, are mixed.It is preferable to homogeneously blend and pulverize the mixture usinga common mixer such as a wet ball mill, or a bead mill or an ultrasonicdevice.

When mixing and pulverizing the raw materials of the target such asmetal oxides, the particle diameter of the mixture after pulverizationis usually 10 μm or less, preferably 3 μm or less, and particularlypreferably 1 μm or less. When the particle diameter of the metalcompounds is too large, it may be difficult to increase the density ofthe target.

The particle diameters of the mixture of the metal compounds used as theraw material of the target after pulverization can be measured accordingto JIS R1619.

(2) Prefiring Step

A prefiring step is optionally provided in order to preliminarily sinterthe mixture of the compounds used as the raw material of the targetafter preparation of such a mixture.

Prefiring can easily increase the density, but may increase the cost.Therefore, it is desirable to increase the density without prefiring.

In the prefiring step, it is preferable to treat the metal oxide mixturewith heat at 500 to 1,200° C. for 1 to 100 hours. If the temperature islower than 500° C. or the period of heat treatment is less than onehour, thermal decomposition of the indium compound, zinc compound, andtin compound may be insufficient. If the temperature is higher than1,200° C. or the period of heat treatment is more than 100 hours, theresulting particles may become large.

Therefore, it is particularly preferable to heat-treat (prefire) themixture at a temperature in a range of 800 to 1,200° C. for 2 to 50hours.

The prefired body obtained in this step is preferably pulverized beforethe following molding step and firing step. The pulverization ispreferably carried out by using a ball mill, a roll mill, a pearl mill,a jet mill, or the like so that the prefired body has a particlediameter in a range of 0.01 to 1.0 μm. If the particle diameter of theprefired body is less than 0.01 μm, the bulk density is too small tohandle the resulting powder with ease. If larger than 1.0 μm, it may bedifficult to increase the density of the target.

The particle diameter of the prefired body can be measured according toJIS R1619.

(3) Molding Step

The molding step is an essential step of press-molding the mixture ofmetal oxides (or the prefired body when the prefiring step is provided)to form the molded product. The product is molded into a form suitableas a target. When the prefiring step is provided, the resulting prefiredpowder may be granulated and the granules may be formed into a desiredshape by press-molding.

Although die molding, cast molding, injection molding, and the like canbe given as the method for molding that can be used in this step, a coldisostatic press (CIP) method or the like is preferable in order toobtain a sintered body (target) with a high sintered density.

A mold assistant agent such as polyvinyl alcohol, methyl cellulose, polywax, and oleic acid may be used in the molding process.

(4) Firing Step

The firing step is an essential step of firing the molded productobtained in the molding step.

The firing can be carried out by hot isostatic press (HIP) firing andthe like.

The firing is carried out in an oxygen atmosphere or under an oxygenpressure at a temperature usually of 700 to 1,700° C., preferably 1,100to 1,650° C., and more preferably 1,300 to 1,600° C. for usually 30minutes to 360 hours, preferably 8 to 180 hours, and more preferably 12to 96 hours. If the firing temperature is less than 700° C., it may bedifficult to increase the density of the target or it may take too longfor sintering. If higher than 1,700° C., the composition may change dueto vaporization of the components or there is a possibility of damagingthe sintering kiln.

If the firing time is less than 30 minutes, it may be difficult toincrease the density of the target. A firing time of more than 360 hoursunduly lengthens the production time and results in high productioncost.

On the other hand, if the powder mixture is sintered in an atmospherenot containing oxygen gas or at a temperature higher than 1,700° C., ahexagonal layered compound may be produced and formation of spinelcrystals (spinel structure compound) may be insufficient, making itdifficult to sufficiently increase the density of the resulting targetand to adequately suppress the abnormal electrical discharge duringsputtering.

The heating rate during firing is usually 20° C./min or less, preferably8° C./min or less, more preferably 4° C./min or less, still morepreferably 2° C./min or less, and particularly preferably 0.5° C./min orless. If the heating rate is more than 20° C./min, a hexagonal layeredcompound may be produced, leading to insufficient formation of spinelcrystals (spinel structure compound).

(5) Reducing Step

A reducing step is optionally provided in order to uniform the bulkresistance of the sintered body obtained in the sintering stepthroughout the entire target by a reducing treatment.

As examples of the reducing method used in this step, a method of usinga reducing gas, a method of reducing by sintering under vacuum, a methodof reducing in an inert gas, and the like can be given.

In the case of the method of using a reducing gas, hydrogen, methane,carbon monoxide or a mixture of these gases with oxygen may be used.

In the case of reduction by sintering in an inert gas, nitrogen, argon,or a mixture of these gases with oxygen may be used.

The reducing treatment is carried out usually at 100 to 800° C., andpreferably 200 to 800° C., for usually 0.01 to 10 hours, and preferably0.05 to 5 hours.

(6) Working Step

A working step is optionally provided to cut the sintered body obtainedby sintering in the above-mentioned manner into a form suitable formounting on a sputtering apparatus and to attach a mounting jig such asa backing plate.

The thickness of the target is usually 2 to 20 mm, preferably 3 to 12mn, and particularly preferably 4 to 6 mm. It is possible to attach twoor more targets to one backing plate to obtain a single target insubstance. The surface is preferably finished using a No. 200 to 10,000diamond wheel, and particularly preferably using a No. 400 to 5,000diamond wheel. If a diamond wheel smaller than No. 200 or larger thanNo. 10,000 is used, the target may be easily cracked.

In the target of the first aspect, it is preferable that the peakposition of the bixbyite structure compound of In₂O₃ shift toward theplus side (wide angle side) relative to the peak position of the X-raydiffraction (XRD) of In₂O₃ powder. The peak shift, at the maximum peakposition (2θ), is preferably 0.05° or more, more preferably 0.1° ormore, and particularly preferably 0.2° or more. In view of the shiftingtoward the plus side (wide angle side), the distance between gratings isprobably short by solid-dissolution substitution of a cation having asmaller ionic radius than indium ion. The peak position of the X-raydiffraction (XRD) of In₂O₃ powder is disclosed in the Joint Committee onPowder Diffraction Standards (JCPDS) database No. 06-0416.

The peak shift angle can be measured by analyzing the X-ray diffractionchart.

If a shift is directed to the minus side (narrow angle side), there is apossibility that carrier generation is insufficient and the targetresistance increases. The reason appears to be that a sufficient amountof carrier electrons are not produced due to an insufficient amount (thenumber of atoms) of other atoms solid-dissolved in In₂O₃.

In the target of the first aspect, the peak position of the spinelstructure compound of Zn₂SnO₄ preferably shifts to the minus direction(narrow angle side). The peak shift, at the maximum peak position (2θ),is preferably 0.05° or more, more preferably 0.1° or more, andparticularly preferably 0.2° or more. The distance between gratings isassumed to be long in view of the shifting to the minus direction(narrow angle side).

If a shift is directed to the plus side (wide angle side), there is apossibility that carrier generation is insufficient and the targetresistance increases. The reason appears to be that a sufficient amountof carrier electrons is not produced due to an insufficient amount (thenumber of atoms) of other atoms solid-dissolved in Zn₂SnO₄.

The peak position of the X-ray diffraction (XRD) of Zn₂SnO₄ powder isdisclosed in the Joint Committee on Powder Diffraction Standards (JCPDS)database No. 24-1470.

Taking unstable supply (scarcity) and hazardous properties of indiuminto consideration, the content of indium in the target of the firstaspect is preferably 69 wt % or less, more preferably 64 wt % or less,and still more preferably 50 wt % or less.

The atomic ratio of zinc to tin (Zn/Sn) in the target of the firstaspect, is preferably in a range of 0.5 to 10, more preferably 0.7 to 7,still more preferably 1 to 4, and particularly preferably 1.1 to 3. Ifthe atomic ratio of zinc to tin (Zn/Sn) is more than 10, the heatresistance under atmosphere may decrease and acid resistance maydecrease. If less than 0.5, the etching rate of the transparentconductive film produced by sputtering may be too small, and fineparticles of tin oxide may be produced in the target, causing abnormalelectrical discharge.

The atomic ratio of zinc to tin (Zn/Sn) can be measured by aninductively coupled plasma (ICP) spectrophotometry.

III. Transparent Conductive Film

The transparent conductive film of the first aspect is formed by thesputtering method using the target of the first aspect.

Although there are no particular limitations to the sputtering methodand the sputtering conditions, the direct current (DC) magnetron method,the alternate current (AC) magnetron method, and the high frequency (RF)magnetron method are preferable. Since a large apparatus is required forapplication to a liquid crystal display (LCD) panel, the DC magnetronmethod and the AC magnetron method are preferable, with the AC magnetronmethod which enables stable film forming being particularly preferred.

Sputtering can be carried out under a pressure usually in a range of0.05 to 2 Pa, preferably 0.1 to 1 Pa, and more preferably 0.2 to 0.8 Pa,under an ultimate pressure usually in a range of 10⁻³ to 10⁻⁷ Pa,preferably 5×10⁻⁴ to 10⁻⁶ Pa, and more preferably 10⁻⁴ to 10⁻⁵ Pa, andat a substrate temperature usually in a range of 25 to 500° C.,preferably 50 to 300° C., and more preferably 100 to 250° C.

An inert gas such as Ne, Ar, Kr, Xe and the like can be usually used asan introduced gas. Of these, Ar is preferable from the viewpoint of ahigh film-forming speed. In the case in which the ratio of zinc to tinis less than I(Zn/Sn<1), inclusion of oxygen in the introduced gas in anamount of 0.01 to 5% is preferable because of easy reduction of thespecific resistance. When the ratio of zinc to tin is more than 2(Zn/Sn>2), inclusion of hydrogen in the introduced gas in an amount of0.01 to 5% is preferable because of easy reduction of the resistance ofthe transparent conductive film.

The transparent conductive film of the first aspect is preferablyamorphous or microcrystalline, with the amorphous transparent conductivefilm being particularly preferable. Whether the transparent conductivefilm of the first aspect is amorphous or not can be confirmed by theX-ray diffraction method. An amorphous transparent conductive filmensures easy etching while suppressing production of etching residue. Inaddition, a uniform film can be obtained even if the area is large.

The etching rate of the transparent conductive film with 45° C. oxalicacid is usually in a range of 20 to 1,000 nm/min, preferably 50 to 300nm/min, more preferably 60 to 250 nm/min, and particularly preferably 80to 200 nm/min. If less than 20 nm/min, not only the tact time may beretarded, but also etching residues may remain. An etching rate of morethan 1,000 nm/min is too fast to control the line width and the like,resulting in fluctuation.

It is desirable for the transparent conductive film of the first aspectto have resistance to PAN which is a metal wiring etching solution. Ifthe transparent conductive film is resistant to PAN, it is possible toetch the metal wiring without melting the transparent conductive filmafter forming a metal wiring material film on the transparent conductivefilm. The PAN resistance is preferably etching with PAN at 50° C. at arate of 20 nm/min or less, and more preferably 10 nm/min or less.

The transparent conductive film of the first aspect has a specificresistance of preferably 1,800 μΩ·cm or less, more preferably 1,300μΩ·cm or less, and particularly preferably 900 Ω·cm or less.

The specific resistance of the transparent conductive film can bemeasured by the four probe method.

The thickness of the transparent conductive film of the first aspect isusually 1 to 500 nm, preferably 10 to 240 nm, more preferably 20 to 190nm, and particularly preferably 30 to 140 nm. If the thickness is largerthan 500 nm, there is a possibility that the film partly crystallizes orit takes a long time to form the film; if smaller than 1 nm, the filmmay be affected by the substrate and may have high specific resistance.The thickness of the transparent conductive film can be measured by thestylus method.

IV. Transference Electrode

The transparent electrode of the first aspect is prepared by etching thetransparent conductive film of the first aspect.

Because the transparent electrode of the first aspect is prepared fromthe transparent conductive film of the first aspect, the transparentelectrode of the first aspect has the above properties of thetransparent conductive film of the first aspect.

There are no specific limitations to the method for etching to preparethe transparent electrode of the first aspect. A suitable etchingsolution, etching method, and etching conditions can be selectedaccording to the purpose and situation.

An etched edge has a taper angle in a range of preferably 35 to 89°,more preferably 40 to 87°, and particularly preferably 45 to 85°. If thetaper angle is less than 35°, the tapered parts may be too large. Thereis a possibility of a reduced open aperture ratio and a short circuit.If more than 89°, the etched edge is reversely tapered. There is apossibility of lowered durability and malfunctioning of panels.

The taper angle at the electrode edge can be measured by observing thecross-section using a scanning electron microscope (SEM).

According to the first aspect, a sputtering target with a lowresistance, a high theoretical relative density, and a high strength canbe provided.

In addition, a transparent conductive film having excellentconductivity, etching properties, heat resistance, and the like andexhibiting resistance to PAN (a mixture of phosphoric acid, acetic acid,and nitric acid) can be provided.

A second aspect of the invention is described below.

I. Sputtering Target (I-1) Constitution of Sputtering Target

The sputtering target of the second aspect (hereinafter referred to as“target of the second aspect”) is characterized by comprising indium,tin, zinc, and oxygen, and only a peak, ascribed to a bixbyite structurecompound is substantially observed by X-ray diffraction (XRD).

The bixbyite structure compound is as previously described in the firstaspect.

“Only a peak ascribed to a bixbyite structure compound is substantiallyobserved by X-ray diffraction (XRD)” means that a peak pattern of No.06-0416 (In₂O₃ single crystal powder) or an analogous (shifted) patternof the Joint Committee on Powder Diffraction Standards (JCPDS) databaseis observed by X-ray diffraction, with the maximum peaks of otherstructures being sufficiently small, i.e. 5% or less of the maximum peakof the bixbyite structure compound, or not substantially observed.

In addition, it is preferable that the peaks of SnO₂ or Sn₃In₄O₁₂observed by X-ray diffraction be sufficiently small, i.e. 3% or less ofthe maximum peak of the bixbyite structure compound, or notsubstantially observed. These compounds, if included, may increase theresistance of the target, tends to easily generate charges on the targetduring sputtering, and may cause abnormal electrical discharge orproduce nodules.

In the target of the second aspect, it is preferable that the atomicratio of In/(In+Sn+Zn) be in a range larger than 0.6 and smaller than0.75, and the atomic ratio of Sn/(Sn+Zn) be in a range of 0.11 to 0.23.

The atomic ratio of In/(In+Sn+Zn) is shown by the inequality formula of0.6<In/(In+Sn+Zn)<0.75, and does not include 0.6 and 0.75.

On the other hand, the atomic ratio of Sn/(In+Sn+Zn) is shown by theformula 0.11≦Sn/(In+Sn+Zn)≦0.23, and includes 0.11 and 0.23.

If the atomic ratio of In/(In+Sn+Zn) is 0.6 or less, the mono layerstructure of the bixbyite structure compound may become unstable and mayproduce other types of crystals; if 0.75 or more, the film produced bysputtering may be easily crystallized, the etching rate may become slow,and residues may be left after etching. In addition, indium reductionmay be insufficient. The atomic ratio of In/(In+Sn+Zn) is morepreferably in a range of 0.61 to 0.69, and still more preferably 0.61 to0.65.

If the atomic ratio of Sn/(In+Sn+Zn) is less than 0.11, the resistanceof the target may increase due to production of the hexagonal layeredcompound of In₂O₃(ZnO)_(m), wherein m is an integer of 2 to 20, and ZnO;if larger than 0.23, Sn₃In₄O₁₂, SnO₂, SnO, and the like may be produced,which may result in an increase of resistance and generation of nodules.

The atomic ratio of Sn/(In+Sn+Zn) is preferably in a range of 0.11 to0.21, more preferably 0.11 to 0.19, and still more preferably 0.12 to0.19.

The atomic ratio of Zn/(In+Sn+Zn) is preferably in a range of 0.03 to0.3, more preferably 0.06 to 0.3, and particularly preferably 0.12 to0.3. If the atomic ratio of Zn/(In+Sn+Zn) is less than 0.03, etchingresidue may remain; if more than 0.3, the heat resistance underatmosphere may be impaired and the film forming rate may decrease.

The above atomic ratios of the target of the second aspect can bemeasured by inductively coupled plasma (ICP) spectrophotometry.

In the target of the second aspect, it is preferable that the peakposition of the bixbyite structure compound to the peak position of theX-ray diffraction (XRD) of In₂O₃ powder shift toward the plus side (wideangle side). When shifting toward the plus side (wide angle side), thetarget is thought to have a short distance between gratings bysolid-dissolution substitution of a cation having a smaller ionic radiusthan the indium ion. The peak position (pattern) of the X-raydiffraction (XRD) of In₂O₃ powder is disclosed in the Joint Committee onPowder Diffraction Standards (JCPDS) database No. 06-0416.

If the shift of the maximum peak position of the bixbyite structurecompound is less than 0.1°, solid dissolution of other atoms in thebixbyite structure compound may become insufficient and other typecrystals may be deposited.

The shift of the peak position of the bixbyite structure compound, interms of the maximum peak position (2θ), is preferably 0.05° or more,more preferably 0.1° or more, and particularly preferably 0.2° or more.

The peak shift angle can be measured by analyzing the X-ray diffractionchart.

FIG. 7 is a chart of the X-ray diffraction of the target of the secondaspect produced in Example 6 mentioned later. The figure indicates thatthe shift of the maximum peak position of the bixbyite structurecompound is 0.4°.

In the target of the second aspect, the average diameter of Znaggregates observed by an electron probe micro analyzer (EPMA) ispreferably 50 μm or less.

If the average diameter of the Zn aggregate is more than 50 μm, the areaof the Zn aggregate serves as a stress concentration point, which mayresult in a decrease of strength, charge generation, and abnormalelectrical discharge.

The average diameter of the Zn aggregate is more preferably 30 μm orless, and still more preferably 15 μm or less.

The ratio of the area of Zn aggregate to the target section area isusually 10% or less, preferably 5% or less, and particular preferably 1%or less.

The content of each of Cr and Cd in the target of the second aspect ispreferably 10 ppm (by mass) or less.

Cr and Cd are impurities of the target of the second aspect. If thecontent of each is more than 10 ppm (by mass), these atoms may serve asnuclei of other types of crystals and it is difficult for the target tohave a bixbyite structure. Moreover, when the formed film is used for aliquid crystal display device, there is a possibility of impairingdurability and causing a burn-in phenomenon.

Excluding the Zn aggregate area, it is preferable that In, Sn, and Zn bedistributed almost homogeneously.

The content of each of Cr and Cd is more preferably 5 ppm or less, andparticularly preferably 1 ppm or less.

The content of each of Fe, Si, Ti, and Cu in the target of the secondaspect is preferably 10 ppm (by mass) or less.

Fe, Si, Ti, and Cu are impurities of the target of the second aspect. Ifthe content of each of these is more than 10 ppm (by mass), other typesof crystals tend to be easily produced and it is difficult for thetarget to have a bixbyite structure.

The content of each of Fe, Si, Ti, and Cu is more preferably 5 ppm orless, and particularly preferably 1 ppm or less.

The content of the above impurity elements can be measured byinductively coupled plasma (ICP) spectrophotometry.

To the extent that the effect of the second aspect is not impaired, itis possible to add Mg, B, and Ga to improve the transmission rate, toadd Al to improve heat resistance, and to add Zr to improve chemicalresistance.

In the target of the second aspect, the diameter of the crystalparticles of the bixbyite structure compound is preferably 20 μm orless.

If the crystal grain diameter of the bixbyite structure compound is morethan 20 μm, the particle boundary serves as a stress concentrationpoint, which may result in a decrease of strength and may easily impairsmoothness of the target surface.

The diameter of the crystal particles of the bixbyite structure compoundis more preferably 8 μm or less, and particularly preferably 4 μm orless.

The crystal grain diameter of the bixbyite structure compound can bemeasured using an electron probe micro analyzer (EPMA).

It is preferable that the target of the second aspect have a bulkresistance of 0.2 to 100 mΩ·cm.

If the bulk resistance is less than 0.2 mΩ·cm, the resistance may becamelower than the resistance of the formed film and scattered film mayproduce nodules. If more than 100 mΩ·cm, sputtering may be unstable.

The bulk resistance of the target of the second aspect is morepreferably in the range of 0.3 to 10 mΩ·cm, still more preferably 0.4 to6 mΩ·cm, and particularly preferably 0.4 to 4 mΩ·cm.

The theoretical relative density of the target of the second aspect ispreferably 90% or more. If the theoretical relative density of thetarget is less than 90%, the target may crack during discharge.

The theoretical relative density of the target of the second aspect ismore preferably 94% or more, still more preferably 95% or more, andparticularly preferably 98% or more.

The deflecting strength of the target of the second aspect is preferably10 kg/mm² or more, more preferably 11 kg/mm² or more, and particularlypreferably 12 kg/mm² or more. Transportation and installation of thetarget are as described in the section of the target of the firstaspect. The target may be damaged due to the load applied duringtransportation and installation. For this reason, the target must have adeflecting strength of a degree not less than a certain level. If thedeflecting strength is less than 10 kg/mm², the target may not beusable.

The method for measuring the bulk resistance, theoretical relativedensity, and deflecting strength of the target are as described in thesection of the target of the first aspect.

(1-2) Production Method of Sputtering Target

The method for producing the sputtering target of the second aspect(hereinafter referred to from time to time as “production method of thetarget of the second aspect”) comprises the steps of preparing a mixtureof raw material compounds of indium, tin, and zinc at an atomic ratio ofIn/(In+Sn+Zn) in a range larger than 0.6 and smaller than 0.75, and anatomic ratio of Sn/(In+Sn+Zn) in a range of 0.11 to 0.23, press-moldingthe mixture to obtain a molded product, heating the molded product at arate of 10 to 1,000° C./hour, firing the molded product at a temperaturein a range of 1,100 to 1,700° C. to obtain a sintered body, and coolingthe sintered body at a rate of 10 to 1,000° C./hour.

Each step of the production method of the target of the second aspectwill be described below.

(1) Mixing Step

The mixing step is an essential step of mixing the raw material metaloxides of the sputtering target.

As the raw materials, a powder of an indium compound with a particlediameter of 6 μm or less, a powder of a zinc compound, and a powder of atin compound having a particle diameter smaller than the particlediameters of the powders of the indium compound and the zinc compoundare preferably used. If the particle diameter of the powder of the tincompound is equivalent to or larger than the particle diameters of thepowders of the indium compound and the zinc compound, SnO₂ may remain inthe target. SnO₂ remaining in the target may possibly make it difficultto produce a bixbyite structure and may increase the bulk resistance ofthe target.

In addition, it is preferable that the particle diameter of the powderof the tin compound be smaller than the particle diameters of thepowders of the indium compound and the zinc compound. More preferably,the particle diameter of the powder of the tin compound is one half orless of the particle diameter of the powder of the indium compound. Itis particularly preferable that the particle diameter of the powder ofthe zinc compound be smaller than that of the powder of the indiumcompound for easy production of the bixbyite structure.

It is preferable to homogeneously blend and pulverize the metal oxidesused as the raw material for producing the target using a common mixersuch as a wet ball mill or a bead mill or using an ultrasonic device.

Oxides of indium, tin, and zinc which are raw materials of the targetmust be incorporated at an atomic ratio of In/(In+Sn+Zn) in a rangelarger than 0.6 and smaller than 0.75, and the atomic ratio ofSn/(In+Sn+Zn) in a range of 0.11 to 0.23. If the ratios are outside theabove ranges, the target of the second aspect having the above-mentionedeffects cannot be obtained.

The indium compound is as described in the first aspect.

When pulverizing the metals oxides of the raw materials of the target,the particle diameter of the metal oxides after pulverization is usually10 μm or less, preferably 3 μm or less, more preferably 1 μm or less,and still more preferably 0.1 μm. When the particle diameter of themetal oxides is too large, it may be difficult to increase the densityof the target.

The particle diameters of the metal compounds used as the raw materialof the target after pulverization can be measured according to JISR1619.

(2) Prefiring Step

A prefiring step is optionally provided in order to preliminarily sinterthe mixture of indium compounds, zinc compounds, and tin compounds usedas the raw material of the target after preparation of such a mixture.

After obtaining a mixture of the indium compounds, zinc compounds, andtin compounds, it is preferable to preliminary fire the mixture.However, in the case of a large target such as that used formanufacturing a liquid crystal panel, the crystal type may not bestable. In such a case, the prefiring step is better omitted.

The heat treatment in the prefiring step is as described in the firstaspect.

The prefired body obtained in this step is preferably pulverized beforemolding and sintering. The pulverization can be carried out in the samemanner as described in the first aspect.

(3) Molding Step

The molding step is as described in the first aspect.

(4) Firing Step

The sintering step is an essential step to fire the molded product,which is obtained by granulating the fine powder obtained in the moldingstep and molding the powder into a desired shape by press-molding. Thefiring step includes the steps of heating the molded product obtained bythe molding step at a temperature in a range of 10 to 1,000° C./hour,firing the molded product at a temperature in a range of 1,100 to 1,700°C. to obtain a sintered body, and cooling the sintered body at a coolingrate of 10 to 1,000° C./hour.

The firing can be carried out by hot isostatic press (HIP) firing andthe like.

The firing is carried out at a temperature usually in a range of 100 to1,700° C., preferably in a range of 1,260 to 1,640° C., more preferablyin a range of 1,310 to 1,590° C., and particularly preferably in a rangeof 1,360 to 1,540° C., for a period of 30 minutes to 360 hours,preferably 8 to 180 hours, and more preferably 12 to 120 hours.

The firing is carried out in an oxygen atmosphere under oxygen pressure.If the raw material powder mixture is fired in an atmosphere notcontaining oxygen gas, gas components such as oxygen dissociate from theraw material during firing and may change the composition. If fired at atemperature of 1,700° C. or more, generation of a hexagonal layeredcompound may be predominant, production of bixbyite crystals may beinsufficient and some of the components may gasify, making it difficultto control the component composition. If the temperature is lower than1,100° C., the objective crystal forms may not be produced. There is apossibility that the sintered body density may not be increased, thetarget resistance may increase, and strength may decrease. If thesintering temperature is lower than 1,100° C., other crystal formshaving high resistance may be produced. There is a possibility that theraw materials may remain and the relative density of the target maydecrease. If the sintering time is shorter than 30 minutes, there is apossibility that the raw materials may remain and the relative densityof the target may decrease.

The heating rate of the molded product is usually 10 to 1,000° C./hour,preferably 20 to 600° C./hour, and more preferably 30 to 300° C./hour.If the heating rate is more than 1,000° C./hour, a hexagonal layeredcompound may be produced, leading to insufficient formation of thebixbyite structure compound. The heating rate of less than 10° C./houris too slow for production and may impair productivity.

The heating rate of the sintered body is usually 10 to 1,000° C./hour,preferably 15 to 600° C./hour, more preferably 20 to 300° C./hour, andparticularly preferably 30 to 100° C./hour. If the heating rate is morethan 1,000° C./hour, a hexagonal layered compound may be produced,leading to insufficient formation of the bixbyite structure and a riskof cracks being produced in the target. The heating rate of less than10° C./hour is too slow for production and may impair productivity.

A cooling rate is preferably less than the heating rate. Morepreferably, a cooling rate is 60% or more, and particularly preferably40% or more, less than the heating rate. A cooling rate smaller than theheating rate ensures production of an objected target in a comparativelyshort period of time.

(5) Reducing Step

The reducing step is as described in the first aspect.

(6) Working Step

A working step is optionally provided to cut the sintered body obtainedby sintering in the above-mentioned manner into a form suitable formounting on a sputtering apparatus and to attach a mounting jig such asa backing plate.

The thickness of the target is usually 2 to 20 mm, preferably 3 to 12mm, and particularly preferably 4 to 6 mm. It is possible to attach twoor more targets to one backing plate to obtain a single target insubstance. The surface is finished preferably using any one of Nos. 80to 10,000 diamond wheels, and more preferably using any one of Nos. 100to 4,000 diamond wheels. Surface finishing using one of Nos. 200 to1,000 diamond wheels is particularly preferable. If a diamond wheel witha smaller number than No. 80 is used, the target may be easily cracked.

Although the use of the above-mentioned production method of the targetof the second aspect is preferable in order to produce the target of thesecond aspect, the method is not particularly limited insofar as the rawmaterials of the target with the above-mentioned particle size are mixedat the above-mentioned specific atomic ratio and processed under theabove-mentioned sintering conditions specified for the firing step(heating rate, cooling rate, sintering temperature, and sintering time).The other steps can be carried out without particularly limitations. Forexample, common methods disclosed in JP-A-2002-69544, JP-A-2004-359984,and Japanese Patent No. 3628554, as well as the following methods can beused. A production method consisting of a combination of some of thesemethods may also be used.

Method of Manufacturing Sputtering Target for Industrial Use (1)

(i) Wet-blend and pulverize weighed raw materials together with waterand adjuvants in a ball-mill, bead mill, etc.(ii) Dry the resulting raw material mixture using a spray dryer, etc.,and granulate to obtain a granule powder.(iii) Press-mold the granule powder, followed by SIP molding using arubber die.(iv) Fire the molded product under oxygen pressure to obtain a sinteredbody.(v) Cut the resulting fired body using a diamond cutter, water cutter,etc. and grind using a diamond wheel, etc.(vi) Apply a wax agent such as metal indium, and secure the resultingtarget to a backing plate made of copper or the like.(vii) Grind the backing plate to remove the wax agent, oxidized layer,etc. and treat the surface of the target.

Method of Manufacturing Sputtering Target for Industrial Use (2)

(i) Dry-blend and pulverize weighed raw materials in a ball mill or thelike to obtain a granule powder.(ii) Press-mold the resulting granular powder.(iii) Sinter the molded product under atmospheric pressure to obtain asintered body.

Method of Manufacturing Sputtering Target for Industrial Use (3)

(i) Dry-blend and pulverize weighed raw materials in a ball mill or thelike to obtain a granule powder.(ii) Wet-blend and pulverize the granule powder in a ball mill,V-blender, etc. to obtain a dispersion of granule powder.(iii) Mold the dispersion of granule powder using a mold die to obtain amolded product.(iv) Dry the molded product by causing contact with air on a supportingbody, and fire under atmospheric pressure to obtain a fired product.

II. Transparent Conductive Film (II-1) Constitution of TransparentConductive Film

The transparent conductive film of the second aspect is prepared byusing the target of the second aspect by the sputtering method.

The transparent conductive film of the second aspect is preferablyamorphous or microcrystalline, and particularly preferably amorphous. Ifthe transparent conductive film is crystalline, the etching rate duringpreparation of a transparent electrode may be slow, residues may remainafter etching, and the taper angle of the electrode terminals may not bewithin the range of 30° to 89° when a transparent electrode is produced.

It is desirable for the transparent conductive film of the second aspectto have resistance to PAN (a mixture of phosphoric acid, acetic acid,and nitric acid) which is a metal wiring etching solution. If thetransparent conductive film is resistant to PAN, it is possible to etchthe metal wiring without melting the transparent conductive film afterforming a metal wiring material film on the transparent conductive film.

(II-2) Production Method of Transparent Conductive Film

The same sputtering method and sputtering conditions as explained in thefirst aspect are applicable to the production of the transparentconductive film of the second aspect.

The transparent conductive film of the second aspect excels inconductivity, etching performance, heat resistance, and the like even ifthe content of indium is reduced. Moreover, the transparent conductivefilm of the second aspect can be etched using a phosphoric acid etchingsolution which is an etching solution for a metal or an alloy. Thisoffers an advantage that the transparent conductive film can be etchedtogether with a metal or an alloy.

The transparent conductive film of the second aspect has a specificresistance of preferably 1,200 μΩ·cm or less, more preferably 900 μΩ·cmor less, and particularly preferably 600 μΩ·cm or less. If the specificresistance is more than 1,200 μΩ·cm, the film thickness must beincreased in order to lower the resistance.

The specific resistance of the transparent conductive film can bemeasured by the four probe method.

The film thickness described in the first aspect is applicable to thefilm thickness of the transparent conductive film of the second aspect.

III. Transparent Electrode (III-1) Constitution of Transparent Electrode

The transparent electrode of the second aspect is prepared by etchingthe transparent conductive film of the second aspect. The transparentelectrode of the second aspect has the above-mentioned characteristicsof the transparent conductive film of the second aspect.

The electrode edge of the transparent electrode of the second aspect hasa taper angle of preferably 30 to 89°, more preferably 35 to 85° andparticularly preferably 40 to 80°. The taper angle at the electrode edgecan be measured by observing the cross-section using a scanning electronmicroscope (SEM).

If the electrode edge has a taper angle of less than 30°, the length ofthe electrode edge portion becomes too long. When a liquid crystal panelor an organic electroluminescence panel is driven, there may be adifference of contrast between the pixel peripheral part and the inside.If the taper angle is more than 89°, the electrode may crack ordelaminate at the edge portion, which may cause defects of an orientedfilm and breakage.

Since the taper angle of the electrode edge can be easily adjusted, thetransparent electrode of the second aspect is particularly suitable foruse on an organic film for which adjustment of the taper angle isdifficult.

(III-2) Method of Preparation of Transparent Electrode

The method for forming a transparent electrode of the second aspect ischaracterized by etching the transparent conductive film of the secondaspect using a 1 to 10 mass % oxalic acid aqueous solution at atemperature of 20 to 50° C. A more preferable concentration of oxalicacid in the oxalic acid-containing solution is 1 to 5 mass %.

According to the production method of the transparent electrode of thesecond aspect, it is preferable to prepare the transparent electrode sothat the taper angle at the electrode edge portion may be 30° to 89°.

The etching rate when a formed transparent conductive film is etched byusing a 5 mass % oxalic acid aqueous solution at 35° C. is usually 10 to500 nm/min, preferably 20 to 150 nm/min, and particularly preferably 30to 100 nm/min. If less than 10 nm/min, not only the tact time isretarded, but etching residues may remain on the resulting transparentelectrode. An etching rate of more than 500 nm/min may be too fast tocontrol the line width and the like.

If the transparent conductive film is resistant to PAN (a mixture ofphosphoric acid, acetic acid, and nitric acid) which is a metal wiringetching solution, it is possible to etch the metal wiring withoutmelting the transparent conductive film after forming a metal wiring onthe transparent conductive film. The PAN resistance allows etching withthe PAN at 50° C. at a rate of preferably 20 nm/min or less, and morepreferably 10 nm/min or less.

According to the second aspect, a sputtering target with low resistance,high theoretical relative density, and high strength can be provided.

According to the second aspect, there can be provided a target capableof performing stable sputtering while suppressing abnormal electricaldischarge generated when forming a transparent conductive film by thesputtering method, even if the indium content is reduced.

According to the second aspect, a transparent conductive film excellingin conductivity, etching properties, heat resistance, and the like, andsuitable for various applications such as a display represented by aliquid crystal display, a touch panel, and a solar cell, can beprovided, even if the content of indium is reduced in the film formed bythe sputtering method for the target of the present invention.

The third aspect of the invention is described below.

The transparent conductive film of the third aspect comprises amorphousoxides of indium (In), zinc (Zn), and tin (Sn). When the atomic ratio ofSn to In, Zn, and Sn is 0.20 or less, In, Zn, and Sn satisfy thefollowing atomic ratio formulas.

0.50<In/(In+Zn+Sn)<0.75 0.11<Sn/(In+Zn+Sn)≦0.20 0.11<Zn/(In+Zn+Sn)<0.34

The atomic ratio of indium (In/(In+Zn+Sn)) is preferably 0.54 to 0.67,more preferably 0.55 to 0.66, and particularly preferably 0.56 to 0.65.If 0.50 or less, the specific resistance may increase and durability ofthe tape carrier package (TCP) connections may decrease when using thetarget as an electrode. If 0.75 or more, the etching rate, when etchedwith an etching solution containing nitric acid, may decrease, residuesmay be left after etching, adjustment of a taper angle may be difficult,adhesion to a metal or an alloy may become poor, and the ratio of theetching rate B when etched with an etching solution containing oxalicacid to the etching rate A when etched with an etching solutioncontaining phosphoric acid (B/A) may decrease.

The atomic ratio of tin (Sn/(In+Zn+Sn)) is preferably 0.12 to 0.20, morepreferably 0.13 to 0.19, and particularly preferably 0.16 to 0.19. If0.11 or less, the etching rate may become too high, making it difficultto control the etching work, the specific resistance may unduly increaseif treated with heat in the presence of oxygen, and durability of TCPconnections may decrease.

The atomic ratio of zinc (Zn/(In+Zn+Sn)) is preferably 0.18 to 0.34,more preferably 0.20 to 0.34, and particularly preferably 0.20 to 0.30.If 0.11 or less, the etching rate may decrease, residues may be leftafter etching, and adhesion to a metal or an alloy may become poor. If0.34 or more, the specific resistance may unduly increase if treatedwith heat in the presence of oxygen and durability of TCP connectionsmay decrease.

When the atomic ratio of Sn to In, Zn, and Sn is more than 0.20, In, Zn,and Sn satisfy the following atomic ratio formulas.

0.30<In/(In+Zn+Sn)<0.60 0.20<Sn/(In+Zn+Sn)<0.25 0.14<Zn/(In+Zn+Sn)<0.46

The atomic ratio of indium (In/(In+Zn+Sn)) is preferably 0.35 to 0.55,and more preferably 0.40 to 0.52. If 0.30 or less, the specificresistance may increase and durability of TCP connections may decrease.If 0.60 or more, the etching rate may decrease when a nitricacid-containing etching solution is used, residues may be left afteretching, and in-plane distribution of the etching rate may increase.

The atomic ratio of tin (Sn/(In+Zn+Sn)) is preferably 0.21 to 0.24, andmore preferably 0.21 to 0.23. If 0.25 or more, the etching rate maydecrease when a nitric acid-containing etching solution is used,residues may be left after etching, and adhesion to a metal or an alloymay be impaired.

The atomic ratio of zinc (Zn/(In+Zn+Sn)) is preferably 0.15 to 0.45. If0.14 or less, the etching rate may decrease, residues may be left afteretching, and adhesion to a metal or an alloy may become poor. If 0.46 ormore, the specific resistance may unduly increase when treated with heatin the presence of oxygen and durability of TCP connections maydecrease.

To the extent that the effect of the third aspect is not adverselyaffected, the sputtering target of the third aspect may contain,aluminum, gallium, magnesium, boron, germanium, niobium, molybdenum,tungsten, yttrium, antimony, hafnium, tantalum, calcium, beryllium,strontium, cesium, lanthanoids, and the like in addition to indium, tin,and zinc.

When preparing an electrode substrate containing a transparentconductive film and a metal or alloy layer, it is preferable that thetransparent conductive film of the third aspect be easily etched with anetching solution for etching a transparent conductive film, but hardlyetched with an etching solution for etching a metal or an alloy.Specifically, it is preferable that the etching rate of the etchingsolution for etching a transparent conductive film be higher than theetching rate of the etching solution for etching a metal or an alloy.

Usually, an etching solution containing a carboxylic acid such as oxalicacid is used as the etching solution for etching a transparentconductive film, and an etching solution containing an oxo acid such asphosphoric acid is used as the etching solution for etching a metal oran alloy.

In the transparent conductive film of the third aspect, the ratio B/A,which is a ratio of the etching rate (B) when etched with an etchingsolution containing oxalic acid to the etching rate (A) when etched withan etching solution containing phosphoric acid, is 10 or more.

The ratio B/A is preferably 15 to 100,000, and more preferably 20 to10,000. If less than 10, a part of the transparent electrode film whereexposed to an etching solution during etching of a metal or an alloy maybecome thin, or the surface may be roughened.

If more than 10,000, the control of the etching rate and taper angle maybecome difficult.

As an etching solution containing phosphoric acid, a mixed acid ofphosphoric acid, nitric acid, and acetic acid is preferable, with a morepreferable etching solution containing 20 to 95 wt % of phosphoric acid,0.5 to 5 wt % of nitric acid, and 3 to 50 wt % of acetic acid. Theetching solution may further contain a surfactant in addition to theseacids. As the surfactant, an anionic surfactant or a nonionic surfactantis preferable, and the anionic surfactant is more preferable. As thesurfactant, an anionic surfactant or a nonionic surfactant ispreferable, and the anionic surfactant is more preferable.

The content of oxalic acid in the etching solution containing oxalicacid is preferably 0.5 to 20 wt %. The etching solution may containdodecylbenzenesulfonic acid, polyoxyethylene phosphate, polysulfonicacid compound and the like. Furthermore, in order to improve wettabilityto the surface of each layer of the multilayer film which is to beetched, a surfactant may be included. As the surfactant, an anionicsurfactant or a nonionic surfactant is preferable, and the anionicsurfactant is more preferable.

As examples of the anionic surfactant, fluorine-based surfactants suchas “Ftergent 110” (manufactured by Neos Co., Ltd.) and “EF-104”(manufactured by Mitsubishi Materials Corp.), nonfluorine-basedsurfactants such as “Persoft SF-T” (manufactured by NOF Corp.), and thelike can be given.

As examples of the nonionic surfactant, fluorine-based surfactants suchas “EF-122A” (manufactured by Mitsubishi Materials Corp.),nonfluorine-based surfactants such as “Ftergent 250” (manufactured byNeos Co., Ltd.), and the like can be given.

The etching temperature is preferably 20 to 50° C.

The etching rate at 35° C. of the etching solution containing oxalicacid is preferably 10 to 1,000 nm/min, more preferably 20 to 500 nm/min,still more preferably 25 to 300 nm/min, and particularly preferably 50to 200 nm/min. If less than 10 nm/min, productivity may be decreased. Ifmore than 1,000 nm/min, there is a possibility that the taper angle andline width cannot be controlled.

The transparent conductive film of the third aspect can be used as atransparent electrode. The end of the transparent electrode prepared byetching with an etching solution containing oxalic acid has a taperangle of preferably 30 to 89°. The taper angle is more preferably 35 to89°, and particularly preferably 40 to 85°.

The taper angle can be controlled by the concentration of the etchingsolution and etching temperature. The etching temperature is preferably15 to 55° C., more preferably 20 to 50° C., and particularly preferably25 to 45° C. If the etching temperature is less than 15° C., the etchingrate may become too small and there is a possibility for generating dewcondensation in equipments. If more than 55° C., water may vaporize andthe concentration of the etching solution is fluctuated.

The transparent conductive film and the transparent electrode of thethird aspect may be formed not only on an inorganic material such asglass or an inorganic insulation film, but also on an organic substrateor an organic film such as a polyimide resin, an acrylic resin, an epoxyresin, a silicon resin, a polycarbonate resin, and a polystyrene resin.Unlike the crystalline membrane such as polycrystal ITO and the like,the transparent conductive film and the transparent electrode of thethird aspect are free from a risk of producing crystalline unevenness onan organic substrate or an organic film. Thus, the transparentconductive film and the transparent electrode are preferably used on anorganic substrate or an organic film. Therefore, the transparentconductive film and the transparent electrode of the third aspect arepreferable as a transparent conductive film and a transparent electrodeused on an organic flattened film such as FSP (field shield pixel).

In the transparent electrode of the third aspect, the atomic ratio oftin and zinc (Sn/Zn) in the connection section (contact point surface)with other conductors, such as a connector (terminal) area with theoutside, is preferably 0.25 to 0.95, more preferably 0.35 to 0.9, stillmore preferably 0.45 to 0.85, and particularly preferably 0.55 to 0.85.If less than 0.25, the connection resistance may be excessive orincreases after a humidity test. If more than 0.95, etching may becomeunstable. The atomic ratio of tin and zinc (Sn/Zn) can be measured byspectral analysis (ESCA).

Moreover, in the transparent electrode of the third aspect, the atomicratio of zinc (Zn/(Zn+Sn+In)) in the connection section (contact pointsurface) with other conductors is preferably 0.01 to 0.35, morepreferably 0.01 to 0.25, still more preferably 0.01 to 0.15, andparticularly preferably 0.05 to 0.15. If less than 0.01, the etchingrate may become low. If more than 0.35, the connection resistance suchas TCP connection may become too large. The zinc atom ratio can beadjusted by a treatment after film formation, the conditions of the filmformation, and the target composition. As the treatment after filmformation, a heat-treatment, laser abrasion, and the like may be used.The zinc atom ratio can be measured by spectral analysis (ESCA).

The electrode substrate of the third aspect preferably comprises thetransparent electrode made of the transparent conductive film of thethird aspect and a layer of a metal or an alloy provided on thetransparent electrode in contact therewith. The layer of a metal or analloy functions as an auxiliary electrode.

The metal or alloy in contact with the transparent electrode comprisesan element selected from the group consisting of Al, Ag, Cr, Mo, Ta, andW, and more preferably comprises Al, Ag, or Mo. These metals may be asingle substance or an alloy containing these metals as a maincomponent. As examples, Ag—Pd—Cu, Ag—Nd, Al—Nd, Al—Nb, Al—Ni, Al—Ti,Al—Ta, and the like can be given.

The electrode substrate of the third aspect is suitable for a displaypanel with an active matrix structure and the like, particularly for aTFT liquid crystal panel. In particular, the electrode substrate can besuitably used for semi-transmissive semi-reflective liquid crystals, VAmode panels, IPS mode panels, OCB mode panels, and FFS mode panels. Theelectrode substrate can also be used for TN system panels and STN systempanels without any problem.

Regarding the TPC connection stability of the transparent conductivefilm of the third aspect, the increase rate of the resistance before andafter a pressure cooker text (PCT) of the TCP connection using ananisotropic conductive film (ACF) is preferably 500% or less, morepreferably 300% or less, and particularly preferably 150% or less.

If more than 500%, the electrode may cause failures such as nonuniformdisplay in a display of a cellular phone used under a stringentcircumstance.

Connection with the outside is not particularly limited to the TPCconnection, but includes other methods of connection such as a chip onglass (COG) connection and chip on film (COF) connection.

The method for producing the electrode substrate of the third aspectcomprises a step of stacking a transparent conductive film, a step ofetching the transparent conductive film with an etching solution for atransparent conductive film, a step of stacking layers of a metal or analloy at least on a part of the transparent conductive film, a step ofetching the layers of the metal or alloy with an etching solution foretching a metal or an alloy.

As the etching solution for etching a transparent conductive film, anetching solution containing a carboxylic acid such as oxalic acid can beused. As the etching solution for etching a metal or an alloy, anetching solution containing an oxo acid such as phosphoric acid can beused.

As the carboxylic acid, a dicarboxylic acid is preferable, and oxalicacid is particularly preferable. As the oxo acid, an inorganic oxo acidis preferable, an inorganic oxo acid containing phosphorus is morepreferable, and phosphoric acid is particularly preferable.

According to the third aspect of the invention, a transparent conductivefilm which has excellent adhesion to a metal or an alloy and can beselectively etched relative to a metal or an alloy can be provided.

According to the third aspect of the invention, a transparent conductivefilm exhibiting a small increase in resistance during a heat treatmentin the atmosphere and a small resistance distribution in a large areacan be provided.

According to the third aspect of the invention, a transparent electrodeand an electrode substrate formed of these transparent conductive filmscan be provided.

According to the third aspect of the invention, a simplified method forproducing an electrode substrate using these transparent conductivefilms can be provided.

EXAMPLES

The invention is described below in more detail by examples. However,the invention is not limited to these examples.

Example 1 (1) Production and Evaluation of Sputtering Target (i)Production of Target

As raw materials for the target, indium oxide with an average particlediameter of 3.4 μm and a purity of 4N, zinc oxide with an averageparticle diameter of 0.6 μm and a purity of 4N, and tin oxide with anaverage particle diameter of 0.5 μm and a purity of 4N were mixed atatomic ratios of In/(In+Sn+Zn)=0.53, Sn/(In+Sn+Zn)=0.17, andZn/(In+Sn+Zn)=0.30. The mixture was supplied to a wet-type ball mill andpulverized for 72 hours to obtain a raw material fine powder.

The resulting fine powder of the raw materials was granulated, and thegranules were press-molded to obtain a molded article with a diameter of10 cm and a thickness of 5 mm. The molded article was put into a firingkiln and fired at 1,400° C. under oxygen pressure for 48 hours to obtaina sintered body (target). The temperature was increased at a rate of 3°C./rain during firing.

(ii) Evaluation of Target

The theoretical relative density, bulk resistance, X-ray diffractionanalysis, crystal grain diameter, and various properties of theresulting target were measured. The X-ray diffraction chart obtained isshown in FIG. 1.

The theoretical relative density of the resulting target was 97%, andthe bulk resistance measured by the four probe method was 1.3 mΩ·cm.

The elementary analysis by ICP spectrometry confirmed the atomiccomposition of In/(In+Sn+Zn)=0.53, Sn/(In+Sn+Zn)0.17, andZn/(In+Sn+Zn)=0.30.

The crystal state in the transparent conductive film material wasobserved by the X-ray diffraction method using a sample collected fromthe sintered body. As a result, only the spinel structure compound ofZn₂SnO₄ and the bixbyite structure compound of In₂O₃ were observed.

As shown in FIG. 1, the maximum peak of the spinel structure compoundshifted by 0.3° to the narrow angle side, and the maximum peak of thebixbyite structure compound shifted by 0.3° to the wide angle side.

The measuring conditions of the X-ray-diffraction measurement (XRD) ofthe target were as follows.

Device: “Ultima-III” manufactured by Rigaku Corp.X rays: Cu—Kα ray (wavelength; 1.5406 Å, monochromized by a graphitemonochromator)2θ-θ reflection method, continuous scan (1.0°/min)Sampling interval: 0.02°

Slit DS, SS: 2/3°, RS: 0.6 mm.

In addition, the resulting sintered body was enveloped in a resin. Aftergrinding with alumina particles with a particle diameter of 0.05 μm, thesurface was inspected by an electron probe micro analyzer (EPMA)(“EPMA-2300” manufactured by Shimadzu Corp.) under the followingconditions.

Accelerating voltage: 15 kVSample current: 0.05 μA

Beam Size: 1 μm Step Size: 0.2×0.2 μm

As a result of measurement under the above conditions, the sintered bodywas confirmed to have a distinct sea-island structure of the indium (In)rich phase and the zinc (Zn) rich phase as shown in FIG. 5, and theratio of the areas S(In) and S(Zn) calculated from each image,S(Zn)/S(In), was 0.9.

Furthermore, the sintered body was enveloped in a resin, and the surfacewas ground using alumina particles with a particle diameter of 0.05 μmand observed by an electron probe micro analyzer (EPMA) (“JXA-8621MX”manufactured by JEOL Ltd.) to measure the maximum diameter of thecrystal particles of the spinel compound observed in a 30 μm×30 μmsquare frame on the surface of the sintered body enlarged to amagnification of 5,000 times. The average value of the maximum particlediameters measured in the same manner in three frames was calculated toconfirm that the crystal grain diameter of the spinel structure compoundof Zn₂SnO₄ and the bixbyite structure compound of In₂O₃ of the sinteredbody was 3.0 μm.

The sintered body obtained in (i) above was cut and processed with a No.400 diamond wheel to prepare a sputtering target with a diameter ofabout 10 cm and a thickness of about 5 mm. The deflecting strength ofthe target was measured to show that the deflecting strength was 13kg/mm². The deflecting strength was measured according to JIS R1601.

(2) Preparation and Evaluation of Transparent Conductive Film (i)Preparation of Transparent Conductive Film

The sputtering target obtained in (1) (i) above was mounted on a DCmagnetron sputtering apparatus to prepare a transparent conductive filmon a glass plate at room temperature.

The sputtering was carried out under the conditions of a sputteringpressure of 1×10⁻¹ Pa, an ultimate pressure of 5×10⁻⁴ Pa, a substratetemperature of 200° C., electrical power of 120 W, and a film formingtime of 15 minutes, while using 100% argon as an introduced gas.

As a result, a transparent conductive glass consisting of a glasssubstrate and a transparent conductive oxide with a thickness of about100 nm formed on the glass substrate was obtained.

(ii) Evaluation of Sputtering State

The sputtering target obtained in (1) (i) above was mounted on a DCmagnetron sputtering apparatus and sputtered under the same conditionsas in (2) (i) above, except that a mixed gas of argon gas and 3%hydrogen gas was used as the introduced gas. Occurrence of abnormalelectrical discharge was monitored during the sputtering to confirm thatno abnormal electrical discharge occurred during continuous sputteringfor 240 hours.

In Table 1, the occurrence of abnormal electrical discharge is indicatedby “Yes” and nonoccurrence is indicated by “No”.

(iii) Evaluation of Nodule Production

Sputtering was carried out continuously for eight hours using thesputtering target obtained in (1) (i) under the same conditions as in(2) (ii) above. The surface of the target after sputtering was observedwith a stereomicroscope at a magnification of 30 times. The number ofnodules with a size of 20 μm or more produced in 900 mm² visual fields,each encircled by three arbitrary points on the target, was counted andthe average was calculated.

(iv) Evaluation of Properties of Transparent Conductive Film

To evaluate the electric conductivity of the transparent conductive filmon the transparent conductive glass obtained in (2)(1) above, thespecific resistance was measured by the four probe method to show thatthe specific resistance was 4×10⁻⁴Ω·cm (400 μΩ·cm).

The transparent conductive film was confirmed to be amorphous by X-raydiffraction analysis.

The measuring conditions of the X-ray-diffraction measurement (XRD) ofthe transparent conductive film were as follows.

Device: “Ultima-III” manufactured by Rigaku Corp.X rays: Cu—Kα ray (wavelength; 1.5406 Å, monochromized by a graphitemonochromator)2θ-θ reflection method, continuous scan (1.0°/min)Sampling interval: 0.02°

Slit DS, SS: 2/3°, RS: 0.6 mm

To evaluate smoothness of the film surface, the P-V value (according toJIS B0601) was measured to indicate that the P-V value was 5 nm,indicating good smoothness.

To evaluate transparency of the transparent conductive film,transmission of a light with a wavelength of 500 nm was measured with aspectrophotometer to confirm that the light transmission was 90%,indicating excellent transparency of the film.

Furthermore, the transparent conductive film was etched with oxalic acidat 45° C. to show that the etching rate was 150 nm/min.

Moreover, the etching rate by PAN (mixed acid of nitric acid: 3.3 mass%, phosphoric acid: 91.4 mass %, and acetic acid: 10.4 mass %), which isa typical phosphoric acid type etching solution for metal wiring, was 20nm/min or less at 50° C., indicating excellent PAN resistance. In Table1, the results of PAN resistance evaluation are indicated as “Good” whenthe etching rate was 20 nm/min or less at 50° C., and as “Bad” when theetching rate was more than 20 nm/min at 50° C.

Examples 2 to 5 and Comparative Examples 1 to 7

The targets and the transparent conductive films were produced andevaluated in the same manner as in Example 1, except for changing thecontent ratio of the raw material metal oxides to make atomic ratiosshown in Table 1. The results are shown in Table 1. X-ray diffractioncharts of the targets obtained in Example 3 and Example 4 arerespectively shown in FIGS. 2 and 3.

The image produced by measuring the sintered body obtained inComparative Example 1 with an electron probe micro analyzer (EPMA) inthe same manner as in Example 1 is shown in FIG. 6.

Since there is a possibility that stable discharge may not be attainedby DC sputtering using the targets obtained in Comparative Examples 2,4, and 5, these targets were used for RF sputtering.

TABLE 1 Example Comparative Example Target (sintered body) 1 2 3 4 5 1 2Atomic In/(In + Sn + Zn) 0.53 0.58 0.34 0.32 0.45 0.31 0.16 ratioSn/(In + Sn + Zn) 0.17 0.24 0.23 0.19 0.24 0.11 0.42 Zn/(In + Sn + Zn)0.30 0.18 0.43 0.49 0.31 0.58 0.42 Ratio of Zn/Sn 1.76 0.75 1.87 2.591.29 5.47 1.00 Sintering Sintering temperature 1,400 1,400 1,400 1,4001,400 1,400 1,400 conditions Sintering period 48 48 48 48 48 48 48 X-rayCrystal In₂O₃ (bixbyite) Yes Yes Yes Yes Yes Yes diffraction formZn₂SnO₄ (spinel) Yes Yes Yes Yes Yes Yes SnO₂ (rutile) Yes ZnO(wurtzite) In₂O₃(ZnO)_(m) (hexagonal Yes Yes layered compound) Sn₃In₄O₁₂Maximum peak ratio 0.5 0.2 1.2 5.5 0.3 — — [I(Zn₂SnO₄)/I(In₂O₃)]Properties Theoretical relative 97 95 100 100 99 85 79 of target density(%) Bulk resistance (mΩ · cm) 1.3 0.7 2.4 4.5 0.9 17 17,000 Deflectingstrength 13 13 15 15 14 11 9 (kg/mm²) Transparent conductive filmCondition Abnormal electrical No No No No No No No of sputter dischargeNodule (number of 0 0 0 0 0 0 0 nodules/8 hr/90 mm²) Properties Specificresistance 400 400 850 900 600 1,100 4,000 of film (μΩ · cm)Crystallinity (X-ray Amorphous Amorphous Amorphous Amorphous AmorphousAmorphous Amorphous diffraction) Speed of etching with 150 60 100 180100 1,000 Insoluble oxalic acid (nm/min, 45° C.) PAN resistance GoodGood Good Good Good Bad Good Comparative Target (sintered body) 3 4 5 67 Atomic In/(In + Sn + Zn) 0.75 0.00 0.42 0.28 0.65 ratio Sn/(In + Sn +Zn) 0.09 0.33 0.58 0.00 0.35 Zn/(In + Sn + Zn) 0.16 0.67 0.00 0.72 0.00Ratio of Zn/Sn 1.85 2.00 0.00 — 0.00 Sintering Sintering temperature1,400 1,400 1,400 1,400 1,400 conditions Sintering period 48 48 48 48 48X-ray Crystal In₂O₃ (bixbyite) Yes Yes Yes diffraction form Zn₂SnO₄(spinel) Yes SnO₂ (rutile) Yes Yes ZnO (wurtzite) Yes In₂O₃(ZnO)_(m)(hexagonal Yes Yes layered compound) Sn₃In₄O₁₂ Yes Maximum peak ratio —— — — — [I(Zn₂SnO₄)/I(In₂O₃)] Properties Theoretical relative 87 78 6072 63 of target density (%) Bulk resistance (mΩ · cm) 60 3,500 150 16 80Deflecting strength 12 9 6 8 7 (kg/mm²) Transparent conductive filmCondition Abnormal electrical No No Yes No Yes of sputter dischargeNodule (number of 0 0 48 0 32 nodules/8 hr/90 mm²) Properties Specificresistance 400 40,000 20,000 3,000 10,000 of film (μΩ · cm)Crystallinity (X-ray Amorphous Amorphous Amorphous Amorphous Crystallinediffraction) Speed of etching with 310 Insoluble Insoluble 10,000Insoluble oxalic acid (nm/min, 45° C.) PAN resistance Bad Good Good BadGood

It can be seen from the results shown in Table 1 that the targetscontaining both the spinel structure compound of Zn₂SnO₄ and thebixbyite structure compound of In₂O₃ have a high theoretical relativedensity, low bulk resistance, and high deflecting strength.

In addition, the transparent conductive films formed by using theabove-mentioned targets are free from abnormal electrical discharge, donot produce nodules, have a low specific resistance, exhibit a moderateoxalic acid etching rate, and possess PAN resistance.

Example 6 (1) Production of Sputtering Target

As raw materials for the target, indium oxide with a purity of 4N and anaverage particle diameter of 2 μm, zinc oxide with a purity of 4N and anaverage particle diameter of 0.6 μm, and tin oxide with a purity of 4Nand an average particle diameter of 0.5 μm were mixed at atomic ratiosof In/(In+Sn+Zn)=0.64, Sn/(In+Sn+Zn)=0.18, and Zn/(In+Sn+Zn)=0.18. Themixture was supplied to a wet-type ball mill and pulverized for 20 hoursto obtain a raw material fine powder.

The resulting fine powder of the raw materials was granulated, and thegranules were press-molded to obtain a molded article with a diameter of10 cm and a thickness of 5 mm. The molded article was put into a firingkiln and fired at 1,400° C. under oxygen pressure for 48 hours to obtaina sintered body (target). The heating rate was 180° C./hr and thecooling rate was 60° C./hr.

(2) Evaluation of Target

The density, bulk resistance, X-ray diffraction analysis, crystal graindiameter, and various properties of the resulting target were measured.As a result, the theoretical relative density was 96%, and the bulkresistance measured by the four probe method was 0.6 mΩ·cm.

The crystal state in the transparent conductive film material wasobserved by the X-ray diffraction method using a sample collected fromthe sintered body. As a result, only the bixbyite structure compound wasfound in the target. In particular, no peak which belongs to SnO₂ orSn₃In₄O₁₂ was found. The chart of X-ray diffraction of the resultingtarget is shown in FIG. 1.

The sintered body was then enveloped in a resin. The surface was groundwith alumina particles with a particle diameter of 0.05 μm and observedwith an electron probe micro analyzer (EPMA) (“JXA-8621MX” manufacturedby JEOL Ltd.) to measure the maximum diameter of the crystal particlesin a 30 μm×30 μm square frame on the surface of the sintered body at amagnification of 5,000 times. The average value of the maximum particlediameters measured in the same manner in three frames was calculated toconfirm that the crystal grain diameter of the bixbyite structurecompound was 2.5/μm.

Elemental analysis of the target confirmed that content of Cr and Cd wasless than 1 ppm.

The sintered body obtained in (1) was cut to prepare a sputtering targetwith a diameter of about 10 cm and a thickness of about 5 mm. Atransparent conductive film was prepared by sputtering using theresulting target.

(3) Preparation of Transparent Conductive Oxide (Transparent ConductiveFilm

A transparent conductive glass consisting of a glass substrate and atransparent conductive oxide with a thickness of 100 nm formed on theglass substrate was obtained in the same manner as in Example 1(2) (i).

(4) Evaluation of Sputtering State

(i) Number of abnormal electrical discharge

Occurrence of abnormal electrical discharge was monitored using thesputtering target obtained in (1) in the same manner as in Example 1(2)(ii). No abnormal electrical discharge was found.

(ii) Number of Nodules Produced

The number of nodules was measured in the same manner as in Example 1(2)(iii) and the average was calculated.

(5) Evaluation of Properties of Transparent Conductive Film

To evaluate the electric conductivity of the transparent conductive filmon the transparent conductive glass obtained in (3) above, the specificresistance was measured by the four probe method to show that thespecific resistance was 500 μΩ·cm.

The transparent conductive film was confirmed to be amorphous by X-raydiffraction analysis. To evaluate smoothness of the film surface, theP-V value (conforming to JIS B0601) was measured to show that the P-Vvalue was 5 nm, indicating good smoothness.

To evaluate transparency of the transparent conductive film,transmission of light with a wavelength of 500 nm was measured by aspectrophotometer to confirm that the light transmission was 90%,indicating excellent transparency of the film.

Furthermore, the transparent conductive film was etched with a 5 mass %oxalic acid solution at 35° C. to indicate that the etching rate was 80nm/min.

In addition, the etching rate using the same PAN as used in Example 1was 20 nm/min or less at 50° C., confirming excellent PAN resistance.

In Table 2, the results of PAN resistance evaluation are indicated by“Good” when the etching rate was 20 nm/min or less at 50° C., and by“Bad” when the etching rate was more than 20 nm/min at 50° C.

The measuring conditions of the X-ray-diffraction measurement (XRD) ofthe target were the same as in Example 1(2) (iv).

Examples 7 and 8 and Comparative Examples 8 to 10

Sputtering targets and transparent conductive films were produced andevaluated in the same manner as in Example 6, except for adjusting theraw material compositions to the atomic ratios shown in Table 2. RFmagnetron sputtering was used for Comparative Example 8. The results ofevaluation are shown in Table 2.

TABLE 2 Example Comparative Example Target (sintered body) 6 7 8 8 9 10Atomic In/(In + Sn + Zn) 0.64 0.67 0.71 0.08 0.64 0.64 ratio Sn/(In +Sn + Zn) 0.18 0.16 0.14 0.46 — 0.36 Zn/(In + Sn + Zn) 0.18 0.17 0.150.46 0.36 — Zn/(Sn + Zn) 0.50 0.52 0.52 0.50 1.00 0.00 SinteringSintering temperature 1,400 1,400 1,400 1,400 1,400 1,400 conditionsSintering period 48 48 48 48 48 48 X-ray Crystal In₂O₃ Yes Yes Yes YesYes Yes diffraction form SnO₂ Yes Yes Sn₃In₄O₁₂ Yes In₂O₃(ZnO)₃ YesIn₂O₃(ZnO)₁₇ Yes Properties Theoretical relative 96 95 93 76 89 85 ofTarget density (%) Bulk resistance (mΩ · cm) 0.6 0.6 0.6 200,000 5 200Deflecting strength 13 13 12 8 11 11 (kg/mm²) Transparent conductivefilm Condition Abnormal electrical No No No No No Yes of sputterdischarge Nodule (number of 0 0 0 0 0 49 nodules/8 hrs/90 mm²)Properties Specific resistance 500 500 500 5,500 600 600 of film (μΩ ·cm) Etching rate (35° C. 80 90 100 <5 200 <5 oxalic acid, nm/min)Crystallinity (X-ray Amorphous Amorphous Amorphous Amorphous AmorphousCrystalline diffraction) PAN resistance Good Good Good Good Bad Good

Example 9

A large target essentially consisting of a bixbyite structure compoundwith the same composition as Example 6 was produced, and an electrodefor a liquid crystal display for television was prepared on an organicfilm by DC magnetron sputtering and oxalic acid etching. A lighting testof the resulting panel prepared by using the electrode was carried outto obtain a performance comparable to a panel in which the electrode wasprepared by using ITO.

No failures such as burn-in occurred during continuous lighting for10,000 hours.

Example 10 (1) Production of Sputtering Target

As raw materials for the target, indium oxide, zinc oxide, and tin oxidewith a purity of 4N and an average particle diameter of 3 μm or lesswere mixed at atomic ratios of In/(In+Sn+Zn)=0.54, Sn/(In+Sn+Zn)=0.18,and Zn/(In+Sn+Zn)=0.28. The mixture was supplied to a wet-type ball milland pulverized for 72 hours to obtain a raw material powder.

The resulting fine powder of the raw materials was granulated and thegranules were press-molded to obtain a molded article with a diameter of10 cm and a thickness of 5 mm. The molded article was put into a firingkiln and fired at 1,400° C. under oxygen pressure for 48 hours to obtaina sintered body (target).

(2) Preparation of Transparent Conductive Oxide Film

The sputtering target obtained in (1) above was mounted on a DCmagnetron sputtering apparatus to prepare a transparent conductive filmon a glass substrate placed on a rotation stage.

The sputtering was carried out under the conditions of a sputteringpressure of 1×10⁻¹ Pa, an oxygen partial pressure (O₂/(O₂+Ar)) of 2%, anultimate pressure of 5×10⁻⁴ Pa, a substrate temperature of 200° C.,electrical power of 120 W, a target-substrate distance of 80 mm, and afilm forming time of 15 minutes.

As a result, a transparent conductive glass consisting of a glasssubstrate and a transparent conductive oxide film with a thickness of100 nm formed on the glass substrate was obtained. The resulting filmwas analyzed by the ICP (inductively coupled plasma analysis) method toconfirm the atomic ratio of In/(In+Sn+Zn) of 0.60, the atomic ratio ofSn/(In+Sn+Zn) of 0.17, and the atomic ratio of Zn/(In+Sn+Zn) of 0.23.The results show a smaller zinc amount than the amount of zinc in thetarget. Although the cause is not completely determined, zinc componentsare assumed to be reversibly sputtered.

(3) Evaluation of Properties of Transparent Conductive Film

To evaluate the electric conductivity of the transparent conductive filmon the transparent conductive glass obtained in (2) above, the specificresistance was measured by the four probe method to indicate that thespecific resistance was 600 μΩ·cm.

The specific resistance was measured after a heat treatment at 240° C.under atmospheric pressure for one hour to indicate that the specificresistance was 650 μΩ·cm. This shows that there was almost no change(1.1 times the initial value) and the transparent conductive film wasstable in the hat treatment under atmospheric pressure. In addition, thespecific resistance was measured at 20 points in-plane of the glasssubstrate to evaluate fluctuation. The difference of the maximum valueand the minimum value was about 1.1 times showing that the specificresistance was remarkably uniform throughout the glass substrate.

The transparent conductive film was confirmed to be amorphous by X-raydiffraction analysis.

The measuring conditions of the X-ray-diffraction measurement (XRD) ofthe target were the same as in Example 1(2) (iv).

To evaluate the smoothness of the film surface, the P-V value(conforming to JIS B0601) was measured to show that the P-V value was 5nm, indicating good smoothness. To evaluate the transparency of thetransparent conductive oxide, transmission of light with a wavelength of500 nm was measured by a spectrophotometer to confirm that the lighttransmission was 90%, indicating excellent transparency of the film.

(4) Evaluation of Etching Properties of Transparent Conductive Film

The transparent conductive film on the transparent electric conductiveglass obtained in the above (2) was etched with an etching solutioncontaining phosphoric acid (phosphoric acid: 87 wt %, nitric acid: 3 wt%, acetic acid: 10 wt %) at 45° C. and an etching solution containingoxalic acid (oxalic acid: 5 wt %, pure water: 95 wt %) at 35° C. todetermine the etching rates.

The etching rate (A) when etched with an etching solution containingphosphoric acid, nitric acid, and acetic acid was 5 nm/min and theetching rate (B) when etched with an etching solution containing oxalicacid was 100 nm/min. The ratio of B/A was 20.

After etching with the etching solution containing oxalic acid, thecross-section was observed with an electron microscope (SEM) and thetaper angle was measured to indicate a taper angle of 80°. Afterover-etching (150%) with the etching solution containing oxalic acid,the cross-section was observed by an electron microscope (SEM) toconfirm that almost no etching residue was left.

(5) Evaluation of Adhesiveness of Transparent Conductive Film and Metal

Adhesion to Mo (molybdenum) was evaluated by a scratch test to show thatthe AE signal standup load was 17 N and the film cracking initiationload was 17 N, confirming excellent adhesion.

The conditions of the scratch test were as follows.

Scratch testing machine: “Micro-Scratch-Tester” manufactured by CSEMScratch distance: 20 mmScratch load: 0 to 30 NLoad rate: 30 N/minScratch rate: 20 mm/minDiamond stylus form: 0.2 mmRDetection method: Load cell and AE sensor

(6) Preparation and Evaluation of Substrate

A 75 nm thick transparent conductive film 12 (FIG. 8( b)) was formed,according to the film-forming method (2) above, on a glass substrate 10using the target of (1) (FIG. 8( a)).

Next, an alloy layer 14 was formed on the transparent conductive film 12using a target of an Ag—Pd—Cu alloy (98.5:0.5:1.0 wt %). The thicknessof the alloy layer 14 was 100 nm.

A sensitizer (resist) was applied to the alloy layer 14. A glass boardwith a mask pattern designed to have a line width of 40 μm and linespace of 70 μm was put on the resist. The resist was exposed to light,developed, and post-baked.

Next, the alloy layer 14 was etched with an etching solution containingphosphoric acid (phosphoric acid: 87 wt %, nitric acid: 3 wt %, aceticacid: 10 wt %) to prepare a plurality of lines (line width: 40 μm, linespace: 70 μm) of the alloy layer 14 (FIG. 8( d)). The resulting blueglass substrate 10 was washed with water and dried.

A sensitizer (resist) was applied to the electrode layer (a lineconsisting of the transparent conductive film 12 and the alloy layer14). A glass board with a mask pattern designed to have a line width of90 μm and line space of 20 μm was put on the resist. The resist wasexposed to light, developed, and post-baked. The resist was exposed tolight so that the line of the alloy layer 14 meets a part (one side) ofthe edge of the transparent conductive film 12 (refer to FIG. 8( e)).

Next, the transparent conductive film 12 obtained above was etched witha 5 wt % aqueous solution of oxalic acid to prepare a number of lines(line width: 90 μm, line space: 20 μm) of the transparent conductivefilm 12 (FIG. 8 (e))

The semi-transmissive semi-reflective electrode substrate obtained inthis manner attained a low electric resistance. The surface of thesubstrate was observed with a scanning electron microscope to confirmthat there was no roughness on the surface of the transparent conductivefilm 12.

This indicates that the transparent conductive film 12 is rarely etchedby an etching solution containing phosphoric acid. In addition, therewas almost no change observed on the edge portion of the alloy layer 14before and after etching with the oxalic acid etching solution.

(7) Connection Stability of Tape Carrier Package (TCP)

TCP resistance before and after the pressure cooker test (PCT) wascompared by TOP connection using an abnormal conductive film (ACF). Theinitial TCP resistance was 4.7Ω, and the TCP resistance after the PCTtest was 4.7Ω, confirming a stable connection.

The TCP resistance is a value of resistance between an arbitrary pair ofwires in TOP connection (connection with a metal terminal electrodehaving a width of 40×10⁻⁶ cm) and is indicated by an average of 50connected parts with the metal terminal by TCP connection.

Example 11 (1) Production of Sputtering Target

As raw materials for the target, indium oxide, zinc oxide, and tin oxidewith a purity of 4N and an average particle diameter of 3 μm or lesswere mixed at atomic ratios of In/(In+Sn+Zn)=0.44, Sn/(In+Sn+Zn)=0.24,and Zn/(In+Sn+Zn)=0.32. The mixture was supplied to a wet-type ball milland pulverized for 72 hours to obtain a raw material powder.

The resulting fine powder of the raw materials was granulated, thegranules were press-molded to obtain a molded article with a diameter of10 cm and a thickness of 5 mm. The molded article was put into a firingkiln and fired at 1,400° C. under oxygen pressure for 48 hours to obtaina sintered body (target).

(2) Preparation of Transparent Conductive Oxide Film

The sputtering target obtained in (1) above was mounted on a DCmagnetron sputtering apparatus to prepare a transparent conductive filmon a glass substrate placed on a rotation stage.

The sputtering was carried out under the conditions of a sputteringpressure of 2×10⁻¹ Pa, an oxygen partial pressure (O₂/(O₂+Ar)) of 2%, anultimate pressure of 5×10⁻⁴ Pa, a substrate temperature of 200° C., atarget-substrate distance of 80 mm, electrical power of 120 W, and afilm forming time of 15 minutes.

As a result, a transparent conductive glass consisting of a glasssubstrate and a transparent conductive oxide with a thickness of 100 nmformed on the glass substrate was obtained. The resulting film wasanalyzed by the ICP method to confirm the atomic ratio of In/(In+Sn+Zn)of 0.50, the atomic ratio of Sn/(In+Sn+Zn) of 0.23, and the atomic ratioof Zn/(In+Sn+Zn) of 0.27. The results indicate a smaller zinc amountthan the amount of zinc in the target. Although the cause is notcompletely determined, zinc components are assumed to be reversiblysputtered.

(3) Evaluation of Properties of Transparent Conductive Film

The properties were evaluated in the same manner as in Example 10(3).The results are shown in Table 4.

(4) Evaluation of Etching Properties of Transparent Conductive Film

The etching properties were evaluated in the same manner as in Example10(4). The results are shown in Table 4.

(5) Evaluation of Adhesiveness of Transparent Conductive Film and Metal

The adhesiveness was evaluated in the same manner as in Example 10(5).The results are shown in Table 4.

(6) Preparation and Evaluation of Substrate

The substrate was prepared in the same manner as in Example 10(6).

The resulting semi-transmissive semi-reflective electrode substrateexhibited a low electric resistance. The surface of the substrate wasobserved with a scanning electron microscope to confirm that there wasno roughness on the surface of the transparent conductive film 12. Thisindicates that the transparent conductive film 12 is rarely etched by anetching solution containing phosphoric acid. In addition, there wasalmost no change observed on the edge portion of the alloy layer 14before and after etching with an oxalic acid etching solution.

(7) Connection Stability of TCP (Tape Carrier Package)

The connection stability was evaluated in the same manner as in Example10(7). The results are shown in Table 4.

Example 12

A sputtering target and a transparent conductive film were produced andevaluated in the same manner as in Example 10, except for adjusting theraw material composition to the atomic ratios shown in Table 3. Theresults are shown in Table 4.

Comparative Examples 11 to 13

Sputtering targets and transparent conductive films were produced andevaluated in the same manner as in Example 10, except for adjusting theraw material compositions to the atomic ratios shown in Table 3. Theresults are shown in Table 4.

Comparative Examples 14 to 16

Sputtering targets and transparent conductive films were produced andevaluated in the same manner as in Example 11, except for adjusting theraw material compositions to the atomic ratios shown in Table 3. Theresults are shown in Table 4.

TABLE 3 Example Comparative Example 10 11 12 11 12 13 14 15 16 AtomicIn/(In + Sn + Zn) 0.54 0.44 0.61 0.60 0.58 0.50 0.50 0.48 0.40 ratioSn/(In + Sn + Zn) 0.18 0.24 0.17 0.40 0.30 0.50 0.40 Zn/(In + Sn + Zn)0.28 0.32 0.22 0.12 0.50 0.12 0.60

TABLE 4 Example Comparative Example 10 11 12 11 12 Atomic In/(In + Sn +Zn) 0.60 0.50 0.68 0.60 0.60 ratio Sn/(In + Sn + Zn) 0.17 0.23 0.16 0.400.30 Zn/(In + Sn + Zn) 0.23 0.27 0.16 0.10 Properties Specific Initialvalue (μΩ · cm) 600 650 450 800 650 of film resistance After heat test(under atmospheric 650 690 480 850 700 pressure, 240° C., 1 hour) (μΩ ·cm) After heat test + initial value (times) 1.1 1.1 1.1 1.1 1.1Distribution (in-plane maximum ÷ 1.1 1.1 1.1 23 6 in-plane minimum(times)) Crystallinity X-ray diffraction Amorphous Amorphous AmorphousMicro- Amorphous crystalline Smoothness P-V value (nm) 5 5 5 10 5 Light(%) 90 90 90 90 87 transmission Etching rate Etching solution containingphosphoric 5 2 3 <1 <1 (A) acid, nitric acid, and acetic acid at 45° C.(nm/min) Etching rate Etching solution containing oxalic 100 60 45Unable to 20 (B) acid at 35° C. (nm/min) etch B/A 20 30 15 Taper angle(Degree) 80 80 85 95 95 (etching with oxalic acid) Etching residueElectron microscope Good Good Good Bad Bad Adhesiveness AE signalstandup load (N) 17 17 16 13 14 Film cracking initiation load (N) 17 1716 13 14 TCP connection Initial value (T0) (Ω) 4.7 4.8 4.2 5.0 4.8stability After PCT (T1) (Ω) 4.7 4.8 4.2 5.0 4.9 Rate of increase (T1/T0× 100) (%) 100 100 100 100 102 Comparative Example 13 14 15 16 AtomicIn/(In + Sn + Zn) 0.57 0.50 0.50 0.50 ratio Sn/(In + Sn + Zn) 0.00 0.500.40 Zn/(In + Sn + Zn) 0.43 0.10 0.50 Properties Specific Initial value(μΩ · cm) 800 850 750 850 of film resistance After heat test (underatmospheric 1,700 900 750 2,400 pressure, 240° C., 1 hour) (μΩ · cm)After heat test + initial value (times) 2.1 1.1 1.0 2.8 Distribution(in-plane maximum ÷ 17 25 8 20 in-plane minimum (times)) CrystallinityX-ray diffraction Amorphous Micro- Amorphous Amorphous crystallineSmoothness P-V value (nm) 5 10 5 5 Light (%) 88 90 86 88 transmissionEtching rate Etching solution containing phosphoric 2,000 <1 <1 2,000(A) acid, nitric acid, and acetic acid at 45° C. (nm/min) Etching rateEtching solution containing oxalic 2,000 Unable to 10 2,000 (B) acid at35° C. (nm/min) etch B/A 1 1 Taper angle (Degree) 25 95 95 25 (etchingwith oxalic acid) Etching residue Electron microscope Good Bad Bad GoodAdhesiveness AE signal standup load (N) 16 12 14 16 Film crackinginitiation load (N) 16 12 14 16 TCP connection Initial value (T0) (Ω)6.5 5.1 4.9 6.7 stability After PCT (T1) (Ω) 90 5.1 5.1 105 Rate ofincrease (T1/T0 × 100) (%) 1,385 100 104 1,567

1. A sputtering target which is composed of a sintered body of an oxidecomprising at least indium, tin, and zinc and comprising a spinelstructure compound of Zn₂SnO₄ and a bixbyite structure compound ofIn₂O₃.
 2. The sputtering target according to claim 1, wherein the atomicratio of In/(In+Sn+Zn) is in a range of 0.25 to 0.6, the atomic ratio ofSn/(In+Sn+Zn) is in a range of 0.15 to 0.3, and the atomic ratio ofZn/(In+Sn+Zn) is in a range of 0.15 to 0.5.
 3. The sputtering targetaccording to claim 1, wherein in an X-ray diffraction (XRD), the ratioof the maximum peak intensity of the spinel structure compound ofZn₂SnO₄ (I(Zn₂SnO₄)) to the maximum peak intensity of the bixbyitestructure compound of In₂O₃ (I(In₂O₃)), I(Zn₂SnO₄)/I(In₂O₃), is in arange of 0.05 to
 20. 4. The sputtering target according to claim 1,wherein, in an X-ray diffraction (XRD), the maximum peak intensity ofthe rutile structure compound of SnO₂ (I(SnO₂)), the maximum peakintensity of the spinel structure compound of Zn₂SnO₄ (I(Zn₂SnO₄)), andthe maximum peak intensity of the bixbyite structure compound of In₂O₃(I(In₂O₃)) have the following relationship: I(SnO₂)<I(Zn₂SnO₄)I(SnO₂)<I(In₂O₃) I(SnO₂)<Max. (I(Zn₂SnO₄), I(In₂O₃))÷10 wherein Max.(X,Y) indicates the larger of either X or Y.
 5. The sputtering targetaccording to claim 1, wherein in an X-ray diffraction (XRD), the maximumpeak intensity of the wurtzite structure compound of ZnO (I(ZnO)), themaximum peak intensity of the spinel structure compound of Zn₂SnO₄(I(Zn₂SnO₄)), and the maximum peak intensity of the bixbyite structurecompound of In₂O₃ (I(In₂O₃)) have the following relationship:I(ZnO)<I(Zn₂SnO₄) I(ZnO)<I(In₂O₃) I(ZnO)<Max. (I(Zn₂SnO₄), I(In₂O₃))÷10wherein Max. (X,Y) indicates the larger of either X or Y.
 6. Thesputtering target according to claim 1, wherein, in an X-ray diffraction(XRD), the maximum peak intensity of the hexagonal layered compound ofIn₂O₃(ZnO)_(m), wherein m is an integer of 2 to 20, (I/In₂O₃(ZnO)_(m)),the maximum peak intensity of the spinel structure compound of Zn₂SnO₄(I(Zn₂SnO₄)), and the maximum peak intensity of the bixbyite structurecompound of In₂O₃ (I(In₂O₃)) have the following relationship:I(In₂O₃(ZnO)_(m))<I(Zn₂SnO₄) I(In₂O₃(ZnO)_(m))<(I(In₂O₃)I(In₂O₃(ZnO)_(m))<Max. (I(Zn₂SnO₄), I(In₂O₃))÷10 wherein Max. (X,Y)indicates the larger of either X or Y.
 7. The sputtering targetaccording to claim 1, wherein, in the image of an electron probe microanalyzer (EPMA), indium rich parts S(In) and lead rich parts S(Zn) forma sea-island structure with a ratio of the areas S(Zn)/S(In) in a rangeof 0.05 to
 100. 8. The sputtering target according to claim 1, whereinthe bixbyite structure compound of In₂O₃ has a crystal grain diameter of10 μm or less.
 9. The sputtering target according to claim 1, of whichthe bulk resistance is in a range of 0.3 to 100 mΩ cm.
 10. Thesputtering target according to claim 1, having a theoretical relativedensity of 90% or more.
 11. A method for producing the sputtering targetaccording to claim 1, comprising the steps of: preparing a mixture of apowder of an indium compound, a powder of a zinc compound, and a powderof a tin compound having a particle diameter smaller than the particlediameters of the powders of the indium compound and the zinc compound atan atomic ratio of In/(In+Sn+Zn) in a range of 0.25 to 0.6, an atomicratio of Sn/(In+Sn+Zn) in a range of 0.15 to 0.3, and an atomic ratio ofZn/(In+Sn+Zn) in a range of 0.15 to 0.5; press-molding the mixture toobtain a molded product; and sintering the molded product.
 12. Atransparent conductive film obtained by sputtering the sputtering targetaccording to claim
 1. 13. A transparent electrode obtained by etchingthe transparent conductive film according to claim
 12. 14. A sputteringtarget comprising indium, tin, zinc, and oxygen with only a peakascribed to a bixbyite structure compound being substantially observedby an X-ray diffraction (XRD).
 15. The sputtering target according toclaim 14, wherein the bixbyite structure compound is shown by In₂O₃. 16.The sputtering target according to claim 14, wherein the atomic ratio ofIn/(In+Sn+Zn) is in a range larger than 0.6 and smaller than 0.75, andthe atomic ratio of Sn/(In+Sn+Zn) is in a range of 0.11 to 0.23.
 17. Thesputtering target according to claim 14, wherein, in an X-raydiffraction (XRD), the maximum peak position of the bixbyite structurecompound shifts toward the plus direction (wide angle side) compared toan In₂O₃ single crystal powder.
 18. The sputtering target according toclaim 14, wherein the average diameter of Zn aggregates observed by anelectron probe micro analyzer (EPMA) is 50 μm or less.
 19. Thesputtering target according to claim 14, wherein the content of each ofCr and Cd is 10 ppm (by mass) or less.
 20. The sputtering targetaccording to claim 14, wherein the content of each of Fe, Si, Ti, and Cuis 10 ppm (by mass) or less.
 21. The sputtering target according toclaim 14, wherein the bixbyite structure compound has a crystal graindiameter of 20 μm or less.
 22. The sputtering target according to claim14, of which the bulk resistance is in a range of 0.2 to 100 mΩ cm. 23.The sputtering target according to claim 14, having a theoreticalrelative density of 90% or more.
 24. A method for producing a sputteringtarget comprising the steps of: preparing a mixture of raw materialcompounds of indium, tin, and zinc at an atomic ratio of In/(In+Sn+Zn)in a range larger than 0.6 and smaller than 0.75, and an atomic ratio ofSn/(In+Sn+Zn) in a range of 0.11 to 0.23; press-molding the mixture toobtain a molded product; heating the molded product at a rate of 10 to1,000° C./hour; firing the molded product at a temperature in a range of1,100 to 1,700° C. to obtain a sintered body; and cooling the sinteredbody at a rate of 10 to 1,000° C./hour.
 25. A transparent conductivefilm obtained by sputtering the sputtering target according to claim 14.26. A transparent electrode obtained by etching the transparentconductive film according to claim
 25. 27. The transparent electrodeaccording to claim 26, having a taper angle at an electrode edge of 30to 89°.
 28. A method for forming a transparent electrode comprisingetching the transparent conductive film according to claim 25 with a 1to 10 mass % oxalic acid aqueous solution at a temperature in a range of25 to 50° C.
 29. A transparent conductive film comprising an amorphousoxide of indium (In), zinc (Zn), and tin (Sn), satisfying the followingatomic ratio 1 when the atomic ratio of Sn to In, Zn, and Sn is 0.20 orless, and the following atomic ratio 2 when the atomic ratio of Sn toIn, Zn, and Sn is more than 0.20; Atomic Ratio 1:0.50<In/(In+Zn+Sn)<0.75 0.11<Sn/(In+Zn+Sn)≦0.20 0.11<Zn/(In+Zn+Sn)<0.34Atomic Ratio 2: 0.30<In/(In+Zn+Sn)<0.60 0.20<Sn/(In+Zn+Sn)<0.250.14<Zn/(In+Zn+Sn)<0.46
 30. The transparent conductive film according toclaim 29, having a ratio of the etching rate B when etched with anetching solution containing oxalic acid to the etching rate A whenetched with an etching solution containing phosphoric acid (B/A) of 10or more.
 31. A transparent electrode comprising the transparentconductive film according to claim 29 with a taper angle of 30 to 89°.32. An electrode substrate comprising the transparent electrodecomprising the transparent conductive film according to claim 29 and alayer of a metal or an alloy.
 33. The electrode substrate according toclaim 32, wherein the metal or alloy comprises an element selected fromthe group consisting of Al, Ag, Cr, Mo, Ta, and W.
 34. The electrodesubstrate according to claim 32, which is to be used for asemi-transmissive, semi-reflective liquid crystal.
 35. The electrodesubstrate according to claim 32, wherein the layer of the metal or alloyis an auxiliary electrode.
 36. A method for producing the electrodesubstrate according to claim 32 comprising the steps of: preparing atransparent conductive film; forming a layer of a metal or an alloy atleast on a part of the transparent conductive film; etching the layer ofa metal or alloy with an etching solution containing an oxo acid; andetching the transparent conductive film with an etching solutioncontaining a carboxylic acid.